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ELECTRIC  FURNACES 


IN   THE 


IRON  AND  STEEL  INDUSTRY 


BY 

DIPL.  ING.  W.  RODENHAUSER,  E.E. 

CHIEF  ENGINEER,  ELECTRIC  FURNACE  DEPARTMENT,  ROCHLING  EISEN  UNO 

STAHLWERKE,  VOLKLINGEN,  GERMANY 
CHIEF  ENGINEER,  GESELLSCHAFT  FCR  ELEKTROSTAHLANLAGEN,  M.  B.  H.,  BERLIN 

J.   SCHOENAWA,  Metallurgist 

FORMERLY  WITH  PRAGER  EISENINDUSTRIE,  KLADNO,  AUSTRIA,  AND 
WORKS  MANAGER  OF  ROCHLING  EISEN  UNO  STAHLWERKE 

AND 

C.  H.  VOM  BAUR,  E.E. 

FORMERLY  CHIEF  ENGINEER  AMERICAN  ELECTRIC  FURNACE  COMPANY 


Translated  from  the  Original  by  the  latter  and  now 
Completely  Rewritten 


THIRD    EDITION,    REVISED 
TOTAL   ISSUE,    FIVE   THOUSAND 


NEW  YORK 
JOHN  WILEY  &  SONS 

LONDON:    CHAPMAN  &  HALL,  LIMITED 

1920 


Copyright,  1913,  1917,  1920,  by 

C.  H.  VOM  BAUR 


PRESS  OF  THE  PUBLISHERS  PRINTING  COMPANY,  NEW  TORK,  U.  8.  A. 


Library 


lot* 


PREFACE  FOR  THIRD  EDITION 


THE  giant  strides  made  in  all  forms  of  essential  industrial- 
ism during  the  Great  War  did  not  neglect  the  electric  furnace. 
Indeed,  it  fared  better  than  even  the  optimists  did  hope.  This, 
taken  together  with  the  practical  uniformly  good  steel  made 
in  them  by  experienced  men,  heat  after  heat,  has  placed  this 
industry  on  a  more  solid  and  dignified  footing.  Added  evi- 
dence of  this  is  the  one  thousand  electric  furnaces  melting 
and  refining  steel  which  are  either  built  or  building.  The 
next  ten  years  will  no  doubt  witness  more  than  double  the 
number  of  electric  furnaces  described  in  this  volume  than 
those  which  are  in  existence  to-day. 

C.  H.  VOM  BAUR. 

NEW  YORK  CITY,  December  6th,  1919. 


PROPEZRTV  OF  THE 

LIBRARY 

CHAMBER  OF  MINES 
AND  OIL 

Los  Angeled,  California 


622973 


PREFACE   TO   THE   SECOND    EDITION 
IN    ENGLISH 


THE  belief  expressed  in  the  writer's  preface  five  years  ago 
has  been  well  borne  out.  To-day  there  are  over  212  electric 
furnaces  in  the  iron  and  steel  industry  in  the  United  States  and 
Canada  out  of  a  total  of  562.  Over  half  a  million  tons  of  electric 
steel  are  being  made  annually  the  world  over,  and  production 
only  started  less  than  a  score  of  years  ago. 

The  average  size  of  furnaces  has  also  steadily  increased, 
together  with  the  number  of  days  they  are  in  operation  yearly. 
Several  newcomers  have  made  their  appearance,  with  the  usual 
pain  and  effort  accompanying  such  creations.  Among  these  it 
is  a  pleasure  to  record  due  credit  to  M.  S.  Vincent,  who  was 
so  largely  responsible  for  bringing  out  the  American  designed 
Rennerfelt.  Cordial  thanks  are  here  also  acknowledged  to 
many  friends  for  valuable  information  and  data,  especially  to 
E.  F.  Cone  for  his  cheerful  help  at  all  times. 

C.  H.  VOM  BAUR. 
NEW  YORK,  September  2ist,  1917. 


PROPETR-TV  OR  THE 

LIBRARY 

CHAMBER  OF  MINES 
AND  OIL 

Los  Angeles,  California 


PROPER-TV  OF-  THE: 
LIBRARY 

CHAMBER  OF  MINES 
AND  OIL 

LosAngeles,  California 

PREFACE  TO  THE  GERMAN  EDITION 


ELECTRIC  furnaces  and  their  use  in  the  manufacture  of  steel 
and  iron  have  been  described  in  books  by  Borchers,  Neumann 
Askenasy,  and  others.  Their  treatises  have  either  described  so 
fully  the  whole  subject  of  electro-metallurgy  that  only  a  very 
small  space  could  be  allotted  to  electric  iron  and  steel,  or  else, 
as  in  Neumann's  volume,  only  a  glance  is  given  at  the  early 
experiments  which  were  made  when  these  furnaces  were  first 
introduced. 

Hence,  there  is  need  for  a  work  thoroughly  describing  electric' 
furnaces,  which  are  designed  only  for  the  steel  and  iron  industry. 

For  practical  reasons  the  book  is  divided  into  two  parts,  of 
which  the  first  deals  with  all  questions  relative  to  the  construc- 
tion of  these  electric  furnaces,  and  the  apparatus  used,  while  the 
other  part  takes  up  the  practical  use  of  electric  furnaces  in  the 
steel  mill  and  all  its  metallurgical  reactions. 

While  undertaking  this  work  the  authors  were  conscious  of 
the  difficulty  of  describing  each  type  of  furnace  entirely  from 
personal  observation.  This  difficulty,  however,  confronts  all 
who  are  similarly  situated,  as  these  electric  furnaces  have  only 
recently  been  introduced  into  the  iron  trades  and  it  is  practically 
impossible  to  know  each  type  from  one's  own  experience. 

As  both  practical  and  theoretical  men  differ  regarding  the 
advantages  of  these  furnaces  for  steel  and  iron  making,  it  is  not 
to  be  expected  from  this  book  that  any  one  type  of  furnace  is 
pictured  as  being  better  than  any  other  type.  Wherever  possi- 
ble, therefore,  results  are  given  which  are  based  on  actual  ex- 
perience, although  much  other  material  has  been  used. 

THE  AUTHORS. 

VOLKLINGEN,  SAAR,  IQII. 

vii 


PREFACE  TO  THE  EDITION  IN  ENGLISH 


THE  preparation  of  this  work  in  English  was  undertaken 
in  the  belief  that  electric  furnaces  for  the  iron  and  steel  industry 
would  have  their  greatest  future  on  the  North  American  Conti- 
nent. Especially  is  this  true  of  furnaces  making  electric  steel. 
Specifications  are  daily  becoming  stricter  for  steel  rails,  steel 
castings,  and  tool  steel.  Electric  steel  rails,  costing  but  little 
more  than  the  ordinary  kind,  are  found  to  be  unbreakable  in 
service,  when  laid  beside  open  hearth  and  Bessemer  rails.  In 
these  latter,  scores  of  breakages  have  occurred  in  one  season. 
The  future  of  electric  steel  rails  consequently  seems  assured. 

Electric  steel  castings  have  also  been  on  the  market  for  the 
past  four  years.  They  are  looked  upon  with  favor  alike  by  the 
foundryman  and  the  customer,  not  only  because  the  highest 
class  of  steel  may  be  made  from  the  cheapest  raw  material,  but 
also  because  of  the  high  percentage  of  good  castings  and  their 
freedom  from  blow-holes. 

The  ability  to  make  homogeneous  tool  steel,  free  from  gases, 
and  at  low  cost,  brought  the  electric  furnace  into  commercial  use 
over  a  decade  ago.  In  this  field  it  promises  to  displace  com- 
pletely the  old  and  small  crucible  pot  which  has  been  in  use  since 
the  year  1740. 

With  these  three  principal  fields  now  open  to  electric  furnace 
products,  it  cannot  be  long  before  all  other  domains  in  the 
use  of  steel  will  be  invaded.  The  cost  of  producing  electric  steel 
is  lower  now  than  that  of  the  crucible  process,  or  of  the  small 
converter  process,  and  even  less  than  that  of  the  open  hearth 
process,  as  practised  with  lo-ton  furnaces  or  under.  A  success 
can,  therefore,  be  confidently  predicted  for  electric  furnaces  and 
their  manufacture  of  iron  and  steel. 

A  few  changes  were  found  necessary,  in  adapting  the  German 
to  the  edition  in  English,  and  some  fresh  material  has  been  added. 


X  PREFACE 

The  translator  gladly  takes  this  opportunity  to  thank  many 
friends  for  information  and  assistance.  Dr.  G.  B.  Waterhouse, 
of  Buffalo,  kindly  gave  the  benefit  of  his  extended  experience  in 
connection  with  the  metallurgy  of  iron  and  steel  as  set  forth  in 
Part  II  of  this  book.  To  Mr.  A.  H.  Strong,  of  New  York,  special 
thanks  are  due  for  valuable  aid  rendered  in  the  various  chapters 
on  induction  furnaces.  Mr.  Magnus  linger,  of  the  transformer 
and  furnace  department  of  the  General  Electric  Company,  very 
kindly  read  the  proofs  of  many  chapters  of  Part  I.  No  one  has 
had  a  larger  or  more  successful  experience  in  building  trans- 
formers and  furnaces  than  Mr.  Unger.  Finally,  thanks  are  due 
to  Dr.  D.  A.  Lyon  for  much  new  material  added,  mainly  to  the 
chapters  on  electric  pig-iron  furnaces. 

C.  H.  VOM  BAUR. 
NEW  YORK,  September  7th,  1912. 


PREFACE  TO  PART  I 

THE  realm  of  Steel  and  Iron  manufacture  has  in  the  past  ten 
years  had  a  new  world  of  possibilities  opened  to  it  by  the  intro- 
duction of  the  electric  furnace.  Before  finding  a  commercial 
foothold  among  ironmasters,  it  was  in  use  making  ferro  alloys. 
Even  earlier  than  this  the  electric  furnace  was  manufacturing 
aluminum  and  calcium  carbide. 

It  has  been  the  aim  of  the  present  publication  on  Electric 
Steel  and  Iron  Furnaces  to  produce  a  book  for  the  practical  man; 
a  comprehensive  manual  of  practical  information,  yet  one  ex- 
plaining the  electric  laws  and  phenomena  involved,  and  the 
scientific  principles  upon  which  the  work  rests.  The  under- 
standing of  these  electrical  laws  is  practically  necessary,  for  in 
electric  furnace  literature  we  constantly  find  assertions  con- 
tradicting the  simplest  of  them.  The  authors  also  hope  in  this 
manner  to  render  the  book  of  service  to  the  general  student  of 
this  branch  of  Electro- Chemical  Engineering,  and  to  state 
especially  the  principal  laws  which  the  construction  and  operation 
of  electric  furnaces  entail,  without  giving  long  mathematical 
discussions.  Short  arithmetical  examples  nevertheless  are  given 
dealing  with  actual  furnace  problems.  Care  has  been  taken  to 
mention  only  those  things  which  have  some  value  in  the  develop- 
ment of  Electric  Steel  and  Iron  furnaces,  rather  than  to  dwell 
upon  theories  of  little  moment.  The  furnaces  most  extensively 
used,  such  as  those  of  Stassano,  Heroult,  Girod,  Kjellin,  and 
Rochling-Rodenhauser  are  described  in  detail,  and  compared 
with  an  ideal  Electric  Furnace.  This  seems  to  be  the  best 
course  to  pursue,  for  in  this  way  an  unfair  criticism  of  the  differ- 
ent systems  can  best  be  avoided. 

In  Chapter  XIV,  "General  Review,"  some  furnace  designs 
are  briefly  discussed  which  have  obtained  only  a  limited  use  or 

xi 


xii  PREFACE 

which  have  not  yet  left  the  experimental  stage,  and  finally,  the 
electric  shaft  furnace  is  described  at  length. 

The  discussions  are  accompanied  by  a  large  number  of  cuts 
and  reproductions. 

The  demands  of  actual  practise  have  always  been  given  the 
greatest  consideration.  Accordingly,  the  latest  results  obtained 
from  good  trials  with  electrodes  in  arc  furnaces  are  mentioned,  as 
are  others  of  the  same  order.  This  volume  should,  therefore,  be 
a  welcome  adviser  to  the  furnace  builder,  the  student,  and  in  fact 
to  anybody  who  is  interested  in  electric  furnaces  for  the  pro- 
duction of  steel  and  iron. 

The  authors  have  written  in  the  hope  that  these  pages  will 
aid  in  the  further  expansion  and  success  of  the  electric  iron  and 
steel  trade. 

WM.   RODENHAUSER. 
VOLKLINGEN,   SAAR,    IQII. 


CONTENTS 


PART  I 

ELECTRIC  FURNACES,  THEIR  THEORY,  CONSTRUCTION, 
AND  CRITICISM 

CHAPTER   I 
HISTORICAL 

PAGE 

Some  data  relating  to  the  development  of  electrical  engineering,    ...  i 

Tests  of  Davy  and  Pepys, 3 

Suggestions  by  Wall, 4 

by  Pichon 4 

by  William  von  Siemens, 5 

by  de  Laval, ; 6 

by  Taussig, 8 

The  electric  furnace  of  Stassano, 8 

of  Heroult, 9 

of  Kjellin 9 

Report  of  the  Canadian  Commission  under  Dr.  Haanel, 9 

The  electric  furnace  of  Girod 10 

of  Rochling-Rodenhauser, 10 

of  Gronwall,  Lindblad  &  Stalhane 10 

CHAPTER   II 
SOME  LAWS  AND  FUNDAMENTAL  PRINCIPLES  OF  ELECTRICITY 

Ohm's  Law, II 

Resistance  of  a  conductor, 1 1 

Units  of  measurement :  Ampere,  volt,  ohm, 12 

Temperature  coefficient, 13 

Conductors  of  the  second  class 15 

Series  connection, 16 

Parallel  connection, 17 

I.  Kirchoff's  Law 19 

Combination  resistances, 20 

Arithmetical  example, .21 

Joule's  Law 23 

The  derivation  of  heat  generated 23 

of  power, 24 

of  work, , 25 

xiii 


xjv  CONTENTS 

CHAPTER   III 
EFFECTS  OF  THE  ELECTRIC  CURRENT 

PAGE 

The  action  of  heat,    ' 26 

1.  Direct  resistance  heating, 26 

Gin,  Electric  furnace  of, 27 

Arithmetical  example  therefore, 28 

Current  density,  permissible  in  copper  conductors, 29 

2.  Induction  heating 32 

3.  Indirect  resistance  heating 32 

Borchers,  Laboratory  furnace  of, 33 

Hera  us,  Laboratory  furnace  of 34 

Girod,  Crucible  furnace  of 35 

Helberger,  Crucible  furnace  of, 35 

4.  Arc  heating 37 

Chemical  action, 37 

Motor  effect 39 

Action  of  two  magnets  upon  each  other 40 

Lines  of  force  of  a  current-carrying  conductor, 41 

Direction  of  lines  of  force 41 

Action  between  a  magnet  and  electrical  conductor, 42 

of  two  electrical  conductors  upon  each  other, 43 

Lines  of  force  of  coils, 44 

Pinch  effect, 44 


CHAPTER   IV 
POWER  FACTOR  (cos<£)  AND  ALTERNATING  CURRENT  THEORY  IN  GENERAL 

Periodicity,  frequency,  cycle, 47 

Line  diagram, 47 

Angular  velocity 48 

Induction,  induced  currents, 49 

Self-induction,  current  of  self-induction, 50 

Phase  difference, 51 

Vector  diagram, 51 

Coefficient  of  self-induction 52 

Apparent  resistance,  54 

Power  in  alternating  current  circuits, 57 

factor,  ....... 58 

Losses  on  account  of  induction  phenomena 59 

Eddy  or  Foucoult  currents, 59 

Hysteresis  losses 60 

Three  phase  current,  polyphase  current, 60 

Star  or  Y  connection 61 

Delta  connection, .....62 


CONTENTS  xv 

CHAPTER   V 
GENERAL  CONDITIONS  FOR  THE  OPERATION  OF  ELECTRIC  FURNACES 

PAGE 

Ad v  antages  of  electric  furnaces, 65 

Demands  made  of  an  ideal  electric  furnace, .  66 

Influence  of  the  kind  of  current, 68 

of  the  frequency, 70 

of  changes  in  the  load, 71 

Regulating  power  of  the  furnace  temperature, 72 

Electric  efficiency, '.      .'....«      .  72 

Furnace  and  hearth  arrangement, .      •      •      •  73 

Influence  of  electric  heating .      .     •.      .  73 

Circulation  of  the  molten  metal, .  75 

Influence  of  water  cooling, ....'...  75 

CHAPTER  VI 
THE  ARC  FURNACES  IN  GENERAL 

The  arc, ...      .      .      ....      .     .      .  77 

Radiation  furnaces,        .     ......      .....      .      .      .  '  .      .      .  79 

Combined  arc  and  resistance  furnaces,    .      .      .......      .      .      .  79 

The  electrodes  of  arc  furnaces, 80 

Current  density  in  electrodes, 82 

Efficiency  of  electrodes, 84 

Burning  away  of  electrodes 89 

Electrode  consumption,    .      .      .      .    • •  .      .      .  89 

coverings,        .      .      ...      .      .    ' .     .      ..-,.',.      .      .      .  97 

cooling,      .      ...      .     .    •  .      ...      .      .    v<     .      .      .  99 

regulation,       .      .      .  •  „     -.      .     ...     .    •' .  •  ;.     .      .      .  102 

Thury  regulator;  Seecle  regulator      ....      .      ...    .     .     ,:-   .  103 

CHAPTER   VII 
THE  STASSANO  FURNACE 

Stassano  shaft  furnace, no 

hearth  furnace, .' 112 

•    rotating  furnace,                      ; 112 

Comparison  with  an  ideal  furnace, 120 

Installation  costs, 124 

Issuing  of  licenses, 124 

CHAPTER   VIII 
THE  HEROULT  FURNACE 

Historical, 125 

The  Furnace, 126 

Comparison  with  an  ideal'furnace 139 

Installation  costs 147 

Issuing  of  licenses 148 


xvi  CONTENTS 

CHAPTER   IX 
THE  GIROD  FURNACE 

PAGE 

Historical, 149 

The  furnace 150 

Comparison  with  an  ideal  furnace, 156 

of  electrode  cross-section  with  a  Girod  and  Heroult        .      .      .  159 

Installation  costs 162 

Issuing  of  licenses, 163 

CHAPTER  X 
THE  RENNERFELT  FURNACE 

Historical 165 

The  furnace, 166 

Comparison  with  ideal  furnace 169 

Installation  costs 173 

Issuing  of  licenses 175 

CHAPTER  XI 
THE  INDUCTION  FURNACE  IN  GENERAL 

Principle  of  the  transformer, .  176 

of  the  induction  furnaces, .  177 

Cylinder  winding,  tube  winding,  disk  winding, 181 

Suggestions  by  de  Ferranti, 181 

by  Colby, *      .  185 

by  Kjellin, ,  .     .      .  185 

by  Frick, 185 

Arrangement  for  lessening  the  stray  fields, 187 

Suggestion  by  Rochling  and  Rodenhauser .    •.  188 

CHAPTER  XII 
THE  KJELLIN  FURNACE 

Historical, 189 

The  furnace, .  189 

Influence  of  the  furnace  contents  on  the  power  factor,       .      .     .      ,      .  194 

Comparison  with  an  ideal  furnace,         201 

Issuing  of  licenses, 208 

CHAPTER  XIII 

THE    ROCHLING-RODENHAUSER   FURNACE 

Its  beginning 209 

The  furnace,       ..   ,  •• .....    .'    . 213 

Regulating  transformers,  auto  transformers 230 

Installation  costs, 239 

Issuing  of  licenses, 240 


CONTENTS  xvii 

CHAPTER  XIV 
THE  ELECTRIC  SHAFT  FURNACE 

PAGE 

The  Stassano  electric  shaft  furnace,  .      .      .     '. 241 

The  Keller  electric  shaft  furnace, 242 

The  Heroult  electric  shaft  furnace, 243 

The  test  furnaces  of  Gronwall,  Lindblad  &  Stalhane 244 

The  Gronwall,  Lindblad  &  Stalhane  electric  shaft  furnace 247 

Influence  of  carbon  on  the  energy  taken  up, 250 

Results  of  operation '»'.",.  251 

Installation  costs, 255 

Issuing  of  licenses, 256 

CHAPTER  XV 
GENERAL  REVIEW 

The  Chapelet  arc  furnace  (Giffre,  Allevard),        .      .     .......      .  257 

The  Keller  arc  furnace  .      .      .      . .     T     .      .  258 

The  Nathusius  arc  furnace,       .      .      .      .      .      .      .      «      .      .      .      .      .  260 

The  Gin  induction  furnace,       . 263 

The  Schneider-Creusot  induction  furnace, 263 

The  Gronwall,  Lindblad  &  Stalhane  induction  and  arc  furnace,       .      .      .  264 

Greaves-Etchells  furnace, ."..'.    .     .     ...    .      .  265 

Snyder  furnace, .      ...  ....      .      .      ..  269 

Greene  furnace, .      ...      ^  .      .      .     ,      .      .  227 

The  Hiorth  combination  furnace  and  induction  furnace,      .      ...      .  272 

Moore  furnace,   .      .      .     '. .-.'..     .     .     .  274 

Booth-Hall  furnace        .     .      .     >     .      .      .      .     .     ...      .      .      .  276 

Vom  Baur furnace,  .     .     .    I;      ....      .     .     .,. 279 

Ludlum  furnace,       .      .     .     .     ;     .      .     .     .      .     .    ".     .     .      .      .  284 

CHAPTER  XVI 
FINAL  CONSIDERATIONS 

Economical -    . 287 

Statistics,      .      .  .  .      .      .      .      .      .      .......     .      .      .      .  291 

PART   II 

A. — MATERIALS  FOR  FURNACE  CONSTRUCTION  AND 
THE  COSTS  OF  OPERATION 

MATERIALS  FOR  FURNACE  CONSTRUCTION 

Their  general  requirements, 292 

"Schamotte"  fire-bricks, 294 

Acid  or  silica  bricks 295 

"  Half  Schamotte "  fire-bricks, 295 

Carbon  bricks  and  carbon  for  ramming  in  place, 295 


xviii  CONTENTS 

PAGE 

Basic  bricks  and  materials  for  ramming  in  place,    .      .....     .      .      .  296 

Chrome  iron  ore .....;.  296 

Dolomite, „.'*......  296 

Dolomite  plant 296 

Tar, 296 

Magnesite  and  magnesite  bricks 297 

Mortar ."     .      .  297 

Fluxes  for  the  rammed  part  of  the  lining, 298 

Form  of  hearth  and  durability  of  lining, 300 

THE  COSTS  OF  OPERATION 

Influence  of  the  kind  of  furnace  on  the  quality  of  steel, 300 

General  operating  costs, 301 

Charge, 301 

Loss  in  working, 302 

Comparison  of  the  heating  cost  in  the  open-hearth  and  electric  furnace,  304 

Comparison  of  the  heating  cost  in  the  crucible  and  electric  furnace,  .  306 

Statistics  concerning  electric  steel  production  in  principal  countries,  .  307 

The  amount  of  power  used  and  its  influence, 308 

Comparison  of  the  heating  cost  in  the  electric  shaft  and  ordinary  blast 

furnace, 310 

Unit  price  for  electric  power, 311 

Slag-making  materials, 312 

Labor, 3-12 

Costs  for  lining  or  furnace  maintenance 313 

Amortization  costs, 314 

Cost  of  electrodes, 315 

Auxiliary  arrangements, 315 

Consumption  of  tools, 316 

Total  costs  of  operation  of  the  electric  shaft  compared  with  the  ordinary 

blast  furnace, 317 

Total  costs  of  operation  of  the  Stassano  furnace, 319 

Total  costs  of  operation  of  the  Girod  furnace, 320 

Total  costs  of  operation  of  the  Heroult  furnace, 322 

Increased  cost  through  desulphurization  by  means  of  Ferro-Silicon, .  .  323 

Total  costs  of  operation  for  the  Rochling-Rodenhauser  furnace,  .  .  .  324 

B—  THE  ELECTRO-METALLURGY  o*  IRON  AND  STEEL 

Introduction, 326 

THE  ELECTRIC  SMELTING  OF  IRON  ORES  WITH  THE  PRODUCTION  OF 
IRON  AND  STEEL 

The  smelting  of  ore  in  the  Stassano  furnace,      .     .     .      .      .      .      .      .  335 

The  smelting  of  ore  in  the  Gronwall,   Lindblad  &  Stalhane  electric 

shaft  furnace, 338 


CONTENTS  XIX 

PAGE 

The  smelting  of  ore  in  the  Rochling-Rodenhauser  induction  furnace,      .  339 

Chemical  balance, 341 

Smelting  results, 343 

Criticism  of  ore  smelting  in  the  electrode-hearth  furnace,        ...      .  349 

The  smelting  of  ore  in  the  electrode  shaft  furnace, 351 

Ore  smelting  tests  in  the  special  Heroult  furnace, 355 

Criticism  of  this  nethod  of  smelting,      .      .      ....     .••    .      .  360 

Ore  smelting  in  the  Gronwall,  Lindblad  &  Stalhane  furnace,      .      .  361 
Efficiency  of  the  furnace,        .      .      ...      .      .     -.      .      .      .      .   368-372 

Criticism  of  the  furnace, .      »     -.      .      .      .  374 

Ore  smelting  in  the  Noble  furnace,  .      .      ....'.     .      .      .  375 

Later  results  in  Sweden, .      ....      ;      .  379 

Ore  smelting  in  the  rebuilt  Noble  furnace, 383 

Metallurgy, .      ....      .  389 

Conclusion, 393 

Pig  iron  from  steel  turnings, 394 

The  future  of  electric  steel,    . 395 

Making  pig  steel  in  the  electric  furnace 396 

THE  USE  OF  THE  ELECTRIC  FURNACE  FOR  MELTING,  FOR  THE  REFINING 

OF  PIG  IRON,  AND  FOR  THE  PRODUCTION  OF  ORDINARY  AND 

SPECIAL  QUALITY  STEEL 

The  impurities  in  steel:  phosphorus,  sulphur,  silicon,  copper,  arsenic, 

carbon,  oxygen,  manganese,  aluminum,  vanadium,  titanium,      .      .  399 
The  slag-producing  materials,  ferro-alloys,  etc.,  used  in  the  electric  fur- 
nace: Ferro-manganese,  ferro-chrome,  ferro-silicon,  lime,  fluor-spar, 

iron  ore,  carbon,     .      ;•     .      .      .      .      .      .      . 410 

The  electric  furnace  as  a  melting  furnace  for  iron  and  steel  and  iron 

alloys  of  every  kind, 412 

Melting  of  pig  iron, 413 

Melting  of  ferro-manganese, 414 

Duplexing  with  the  cupola 416 

The  electric  furnace  as  a  mixer,          422 

The  electric  malleable  casting,      .      .  •  ..      .      . 420 

Pig-iron  refining,      .      .      .      . 423 

Production  of  special  quality  steel  in  the  electric  furnace,       .      ...      .  427 

From  previously  refined  metal  with  low  phosphorus  and  sulphur,    .  428 
From  previously  refined  metal  with  considerable  phosphorus  and 

sulphur, .      .   ,.  432 

The  metallurgical  course  of  operations  of  an  electric  furnace  charge,     .  437 

The  special  qualities  of  electric  iron  and  steel,  ........  438 

Final  considerations, 440 

Comparison  of  heating  costs  in  the  open-hearth  and  electric  furnace,     .  442 

INDEX, 445 


xxi 


INDEX   TO    ABBREVIATIONS    USED    IN 
PART   ONE 

A  =  Work  or  Energy. 
Cos  <f>  =  Power  factor. 

E  =  Potential  per  phase. .  j 

e  =  Potential  in  volts  =  Effective  value  for  A.  C. 
e  =  Maximum  value  of  potential, 
e'  =  Instantaneous  value  of  potential. 
6L  =  Potential  to  overcome  the  self-induction. 
er  =  Potential  to  overcome  the  ohmic  resistance. 
I  =  Current  per  phase. 

i  =  Current  in  amperes  =  Effective  value  for  A.  C. 
ir  =  Watt  component  of  current. 
im  —  wattless  component  of  current. 

k  =  Heat  conductivity. 
KVA  =  Kilovolt- amperes. 
KW  =  Kilowatt. 
KW  Hr  =  Kilowatt  hours. 
L  =  Self-induction. 
1  —  Length  of  a  conductor  in  metres, 
m  =  Angular  velocity. 
N  =  Flux, 
p  =  Power. 

p'  =  Instantaneous  value  of  power. 
Q  =  Energy  in  heat  units, 
q  =  Section  in  square  millimetres, 
r  =  Resistance  in  ohms. 
a  —  Turns. 
T  =  Time  of  a  cycle, 
t  =  Time. 
VA  =  Volt  amperes. 

A  =  —  =  Current  density  per  square  millimetre. 

v  =  Cycles  per  second. 

p  =  Specific  resistance  per  I  metre  length  and  I  square  millimetre 
section. 

—  =  Specific  conductivity. 
P 

pi  =  mean  electrical  resistivity  per  cubic  centimetre. 
pi  =  Mean  electrical  resistivity  per  cubic  inch. 

—  =  x  =  Specific  conductivity  per  centimetre. 
Pi 

T  =  Temperature  gradient. 

d  =  Diameter. 


PART  I 

ELECTRIC   FURNACES 

Their  Theory,   Construction  and  Criticisms 


ELECTRIC   FURNACES 
IN  THE  IRON  AND  STEEL  INDUSTRY 


Part    One 


CHAPTER   I 

HISTORICAL  REVIEW 

GREAT  interest  is  today  manifested  in  electric  steel  and  its 
production.  Not  only  are  the  different  iron  and  steel  works 
installing  electric  furnaces  or  considering  their  adoption  when 
enlargements  become  a  good  investment,  but  political  economists 
are  also  carefully  following  the  progress  made  in  the  electric- 
steel  industry.  The  daily  press  frequently  contains  accounts  of 
the  importance  of  electric  iron  and  steel.  Considering  the  great 
and  almost  universal  interest  shown  today  in  the  new  industry,  it 
must  seem  astonishing  that  but  fifteen  years  ago  hardly  a 
thought  was  given  to  the  practical  utilization  of  the  electric 
furnace  for  producing  steel.  This  remarkable  growth  originat- 
ing in  the  laboratory  seems  to  justify  us  in  following  the  de- 
velopment of  the  electric  furnace,  and  in  tracing  the  causes 
which  have  made  its  entrance  into  the  great  industries  possible. 

In  the  first  instance  we  must  clearly  understand  that  all 
electric  furnaces  are  naturally  apparatus  in  which  electrical 
energy  is  consumed  for  the  purpose  of  transforming  it  into  heat. 
Their  development  on  a  large  scale  was  therefore  not  possible 
until  electrical  engineering  had  succeeded  in  producing  sources 
of  current  which  furnished  it  economically,  continuously  and  .of 
sufficient  size. 

At  the  beginning  of  the  last  century  thermopiles,  or  galvanic 
cells,  as  they  are  used  today  for  operating  house  bells,  or  telephone 


2        ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

circuits,  were  the  only  sources  of  electric  current  at  the  disposal 
of  the  user  of  electricity,  so  that  we  see  the  electric  current  of 
this  period  confined  in  its  application  to  the  laboratories  of  the 
scientist.  It  was  only  toward  the  middle  of  the  igth  century 
that  a  strong  development  started  which  has  its  foundation  in 
Faraday's  discovery  of  induction. 

In  1831  Faraday  found  that  each  time  he  brought  a  strong 
magnet  near  to,  or  moved  it  away  from,  a  coil  of  wire,  the  ends  of 
which  were  separated  a  very  small  distance  from  each  other,  a 
tiny  spark  appeared  at  the  point  of  interruption.  We  say, 
therefore,  that  Faraday  found  that  the  magnet  induces  a  current 
in  the  electric  conductor  (the  coil  of  wire). 

This  discovery  brought  a  great  light  into  the  darkness  which 
until  then  had  covered  the  practical  generation  of  electricity; 
for,  hardly  a  year  after  Faraday's  discovery,  we  find  the  first 
magnet-electric  machine,  which  was  built  by  Pixii.  This  was 
the  first  form  of  a  dynamo  machine,  that  is,  of  a  machine  which 
transforms  rotary  motion  into  electric  energy.  In  Pixii's  ma- 
chine a  coil  of  wire  was  arranged  in  the  magnetic  field  of  a  strong 
ordinary  horseshoe  magnet,  in  such  a  way  that  when  the  coil 
was  rotated,  induced  currents  were  produced,  as  discovered  by 
Faraday.  This  first  machine  was  soon  followed  by  improved 
designs,  which,  even  at  this  early  period  of  electrical  science  in 
the  fifties  of  the  last  century,  were  put  to  use  in  supplying  light 
in  lighthouses  on  the  coasts  of  France  and  England. 

The  next  step  forward  was  accomplished  by  H.  Wilde  in  1866 
in  Manchester,  by  the  construction  of  an  electric  machine,  whose 
magnets  were  electro-magnets.  For  these  a  small  machine 
with  ordinary  magnets  furnished  the  current. 

A  Wilde  generator  of  this  type,  which  required  about  3  h.  p. 
for  driving  the  exciting  machine  and  about  1 5  h.  p.  for  the  main 
dynamo,  was  able  to  melt  a  bar  of  platinum  6  mm.  thick  (about 
y^  inch)  and  60  cm.  (two  feet)  long. 

The  above  mentioned  electric  magnetic  machines  were, 
however,  despite  their  considerable  power,  unable  to  introduce 
electricity  for  general  uses.  An  important  forward  step  was 
still  lacking  until  Werner  von  Siemens  discovered  the  "dynamo 


HISTORICAL  3 

electric  principle,"  which  he  laid  before  the  Berlin  Academy  on 
January  17,  1867.  According  to  this  principle  the  "residual" 
magnetism  that  remains  in  even  the  softest  iron  is  sufficient  to 
produce  an  extremely  weak  current  by  which  the  magnetism 
can  be  strengthened  more  and  more.  The  employment  of  this 
discovery  in  the  construction  of  dynamos  now  made  it  possible 
to  use  electro-magnets  instead  of  the  ordinary  permanent  magnets 
heretofore  used,  and,  with  this  improvement,  we  have  the  dynamo 
as  it  is  today.  It  is  used  the  world  over,  following  the  Siemens 
principle. 

But  even  after  Siemens'  discovery  considerable  time  elapsed 
before  any  great  change  occurred  in  the  output  of  large  electric 
generators.  It  was  the  invention  of  the  incandescent  lamp, 
first  generally  known  in  Europe  through  the  Paris  international 
electric  exhibition  in  1881,  which  brought  about  this  develop- 
ment. Electrical  power-houses  in  ever  increasing  numbers  and 
sizes  now  appeared,  and  today  we  see  them  in  nearly  every  city. 
If  we  finally  call  to  mind  the  well-known  first  great  power  trans- 
mission of  a  current  at  30,000  volts  pressure  over  a  distance  of 
170  km.  (106  miles),  between  Lauffen  and  Frankfurt,  Germany, 
which  was  shown  to  the  world  in  1891  at  the  time  of  the  Frank- 
furt Exhibition,  we  find  ourselves  in  the  midst  of  tremendous 
advances  of  electrical  science. 

If  we  now  turn  to  the  history  of  the  development  of  the 
electric  furnace  itself,  we  find  its  first  traces  at  the  beginning  of 
the  i gth  century;  that  is,  at  the  same  time  in  which  the  sole 
means  of  producing  electric  currents  was  the  thermopile,  and  at 
which  time  no  thought  of  any  electrical  science  existed.  The 
first  to  consider  the  practical  exploitation  of  electric  energy  by 
converting  it  into  heat,  probably  was  Davy,  who,  about  1810, 
during  his  experiments  in  the  electrolysis  of  aluminum  oxide,  ex- 
cluded any  influx  of  heat  from  the  outside,  and  produced  the 
heat  necessary  for  the  experiment  by  the  electric  current  itself, 
which  he  obtained  from  an  apparatus  naturally  very  inferior, 
from  the  view-point  of  our  modern  ideas.  His  apparatus  consist- 
ed of  a  platinum  plate  connected  with  one  pole  of  a  thermopile 
of  1000  plates,  the  other  pole  being  connected  with  an  iron  wire. 


4        ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  latter  projected  from  the  upper  side  into  a  layer  of  clay 
carried  by  the  platinum  plate,  which  was  in  connection  with  the 
other  pole.  When  the  circuit  was  established  the  iron  wire 
became  white  hot.  and  melted  where  it  was  in  contact  with  the 
clay. 

A  far  more  perfected  arrangement  was  that  of  Pepys,  who 
in  1815  welded  an  iron  wire  by  heating  it  with  an  electric  current. 
Pepys'  apparatus  can  be  looked  upon  as  the  first  form  of  the 


FIG.  i. 

class  of  electric  furnaces  today  known  as  resistance  furnaces.  A 
soft  iron  rod  was  slotted  with  a  fine  saw  in  the  direction  of  its 
axis  and  the  slot  was  filled  with  diamond  dust.  The  rod  was 
then  wound  with  wire  and  heated  to  red  heat  for  6  minutes  by 
means  of  an  electric  battery  (Fig.  i).  An  examination  of  the 
iron  wire  showed  that  the  diamond  dust  had  disappeared,  and 
that  the  iron  had  changed  with  the  absorption  of  carbon.  In 
this  experiment  iron  was  for  the  first  time  treated  by  the  applica- 
tion of  electric  heat. 

It  is  interesting  to  find  that  in  1843  A.  Wall  made  the  suggest- 
ion that  pig  iron  be  treated  and  converted  by  electrical  means. 
In  1853,  IO  years  later,  we  find  in  a  French  patent  granted  to 
Pichon,  the  first  electro- thermic  furnace.     The  patent  claim  is 
as  follows:    "economical  and  application  of  the  electric  light  to 
metallurgy  and  particularly  metallurgy 
of  iron."      The  furnace  reproduced  by 
Fig.   2   shows   the  original   design  of  a 
furnace    indirectly    heated    by    electric 
arcs.      Such  furnaces  are  used  even  to- 
day with  some   changes  in  the  design 
given   us    by    Stassano.       The   ore  or 
metal  which  Pichon  tried  to  melt  in  his 

furnace  was  dropped  between  electrodes  of  considerable  area 
through  which  the  electric  current  passed.  It  was  expected 


HISTORICAL  5 

that  the  charge  would  melt  under  the  influence  of  the  tempera- 
ture of  the  arc,  and  collect  in  the  bottom,  which  in  turn  was  to 
be  heated.  Pichon's  idea  was  to  build  his  type  of  furnace  on  a 
large  scale,  this  being  clearly  indicated  by  the  dimensions  of  the 
electrodes  which  were  to  be  3  m.  (10  ft.)  long  and  to  have  a 
cross-section  of  60  sq.  cm.  (9.3  sq.  inches). 

It  is  interesting  to  observe  that  Pichon's  suggestion  appeared 
exactly  at  the  time  in  which  the  first  attempts  were  being  made 
to  illuminate  the  sea-coasts  by  means  of  electric  light  supplied 
by  permanent  magnet-electric  dynamos.  Electrical  science, 
which  thus  called  this  furnace  into  existence,  was,  however, 
unable  to  further  the  realization  of  Pichon's  daring  plans,  so 
capable  of  life  as  later  developments  show.  The  magnet-electric 
machine  was  by  a  large  margin  incapable  of  furnishing  the  current 
necessary  for  the  operation  of  Pichon's  furnace. 

Many  different  schemes  were  tried,  in  the  years  immediately 
following  Pichon,  to  utilize  the  electric  current  in  the  production 
of  iron,  but  they  failed,  being  in  advance  of  their  time.  The 
English  patents  of  William  von  Siemens,  of  the  years  1878  and 
1879,  next  bring  developments  in  the  design  of  electric  furnaces. 
They  contain  nearly  all  the  important  details  of  the  modern  arc 
furnaces,  and  for  this  reason  they  will  be  examined  somewhat 
more  closely.  Siemens  used  different  types  of  furnaces.  The 
first  design  consisted  of  a  crucible  surrounded  by  a 
metallic  case,  through  the  bottom  of  which  pro- 
jected one  pole  of  an  electric  circuit.  That  part 
of  the  electrode  in  direct  touch  with  the  charge 
was  provided  with  a  point  of  platinum  or  other 
substance  capable  of  resistance  of  great  heat,  in 
order  to  avoid  contaminating  the  charge.  The 
second  electrode,  which  was  connected  with  the 
other  pole  of  the  electric  circuit,  entered  through 
the  cover  of  the  furnace  and  was  cooled  with 
water  or  other  liquid.  Figure  3  shows  the  arrangement  of  the 
furnace.  Siemens  later  changed  the  design,  making  the  elec- 
trode, which  entered  from  the  top,  of  carbon,  while  the  lower 
metallic  electrode  was  cooled  with  water.  A  heat-protecting 


6        ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


FlG.  4. 


covering  was  provided  for  this  furnace.  The  crucible  was 
placed  in  a  larger  case  of  metal  and .  the  space  between  the 
two  filled  with  charcoal  or  other  poor  conductor  of  heat,  as 
shown  in  the  design,  Fig.  4. 

Siemens  finally  used  a  form  of  furnace 
very  similar  to  that  of  Pichon.  Two  carbon 
electrodes  were  inserted  in  the  sides  of  a 
crucible  in  such  a  position  that  they  remained 
above  the  top  of  the  charge,  and  the  arc 
formed  between  them  did  not  come  in  con- 
tact with  the  material  to  be  melted.  This 
furnace  is  shown  in  Fig.  5.  With  it  Siemens 
succeeded  in  melting  10  kg.  (22  Ibs.)  of 
steel  per  hour.  He  also  reduced  iron  ore 
and  fused  metals  of  high  melting  point  such  as  platinum,  taking 
about  one-quarter  of  an  hour  to  liquefy  4  kg.  (8.8  Ibs.)  of 
the  latter  substance.  Siemens  figured  theoretically  that  the 
combustion  of  i  kg.  of  coal  under  the  boilers  of  a  dynamo- 
electric  generating  plant  would  produce  i  kg.  of  melted  steel. 

Siemens'  furnaces,  in  regard  to  their  practical  construction, 
attained  a  high  degree  of  perfection.  They  were  equipped  with 
automatic  devices  for  adjusting  the  carbons  and  to  keep  the  arc 
length  always  the  same.  He  also  utilized  the  directive  qualities 
of  the  electro-magnet  in  order  to  obtain 
the  best  heating  effects.  All  modern 
constructions  of  arc  furnaces  are  adapta- 
tions of  this  original  design,  differing 
simply  in  size  and  form  and  other  minor 
respects.  The  reason  why  the  Siemens 

furnace  failed  of  successful  introduction  on  a  commercial  scale, 
lies  in  the  fact  that  current  was  still  too  expensive;  it  cost 
too  much  in  those  days  to  be  of  use  in  melting  iron  in  electric 
furnaces. 

With  the  suggestions  of  Siemens,  the  furnace  subject  seemed 
for  the  time  exhausted.  Aside  from  a  long  list  of  unimportant 
patents  the  ensuing  time  shows  no  progress  until  the  appearance 
of  the  interesting  patent  of  de  Laval,  of  the  year  1892.  Fig.  6 


HISTORICAL 


shows  this  furnace.  The  hearth  of  a  cylindrical  furnace  is 
divided  into  two  parts  by  a  bridge  cooled  with  water.  At  the 
bottom  of  each  of  the  two  compartments  metal  or  carbon  elec- 
trodes are  inserted  and  connected  with  a  source  of  alternating 


FIG.  7. 


FIG.  8. 


current.  The  furnace  was  to  be  charged  from  the  top  by  re- 
moving the  cover  and  first  introducing  a  quantity  of  molten 
magnetic  oxide  of  iron.  The  succeeding  charges  were  to  be  of 
spongy  iron. 

In  operating  the  furnace  it  was  intended  to  cover  the  bridge 
with  a  layer  of  oxide  or  other  fusible  substance  which  would  act 
as  a  resistance.  With  an  iron-refining  furnace  oxidized  iron  was 
to  be  used.  The  object  sought  was  to  have  the  spongy  iron 
undergo  a  refining  process  in  falling  through  the  material  forming 
the  resistance;  and  this  was  the  purpose  for  which  de  Laval's 
furnace  was  designed.  De  Laval  saw  a  great  future  for  this 
furnace  and  the  extent  of  his  hopes  can  best  be  realized  from  the 
fact  that  with  Nobel,  in  1895,  he  laid  plans  for  a  power  plant  of 
some  35,000  h.  p.,  to  be  used  in  melting  iron  by  electricity. 
These  bright  hopes  failed  of  realization,  and  de  Laval's  furnace 
has  today  an  historical  interest  only,  as  the  first  example  of  a 
furnace  to  melt  iron  by  direct  resistance.  But  the  plans  show 
that  we  have  arrived  at  an  epoch  in  the  development  of  electro- 
chemistry, by  aid  of  which,  and  that  of  great  water-power  it  is 
possible  to  consider  operating  electric  furnaces  on  a  large  scale. 


8        ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Another  type  of  resistance  furnace,  the  Taussig,  appeared  in 
1893.  No  longer  is  a  separate  liquid  resistance  required.  The 
charge  itself,  whether  metal  or  ore,  forms  the  resistance,  and  in 
consequence  the  furnace  takes  the  shape  of  a  horizontal  groove 
rather  than  a  vertical  one  as  Fig.  7  shows.  This  furnace  also 
remained  unused.. 

It  is  evident  from  the  above  that  in  the  middle  of  the  nineties 
of  the  last  century  there  existed  a  number  of  designs  for  electric 
furnaces,  and  that  the  process  of  heating  metal  baths  by  elec- 
tricity was  well  understood.  But  the  iron  industry  had  so  far 
refused  to  take  the  electric  furnace  seriously.  This  is  even  more 
astonishing  considering  the  pathfinding  and  successful  employ- 
ment of  the  Heroult  furnaces  of  1887  and  1888  in  the  aluminum 
industry,  and  the  use  of  the  electric  furnace  in  the  manufacture 
of  calcium  carbide  in  1894.  Both  these  industries  had  already 
attained  their  full  growth  when,  with  the  new  century  at  last, 
the  interest  of  the  iron  industry  in  the  electric  furnace  began  to 
awaken.  The  main  reasons  for  this  late  beginning  of  the  electro- 
steel  and  electro-iron  industries  may  be  sought,  first,  in  the 
high  development  of  the  existing  process  for  the  manufacture 
of  steel  and  iron,  which  seemed  to  preclude  any  possibility 
of  cheapening  steel;  and,  second,  in  the  fact  that  nothing 
definite  was  known  about  the  quality  of  the  product  of  the 
electric  furnace. 

The  first  practical  constructions  of  furnaces  to  melt  and 
refine  iron  appeared  at  the  same  places  where  the  iron  industry 
itself  had  come  into  being;  that  is,  places  having  favorable 
water-power.  Here  the  electric  furnaces  could  obtain  cheap 
current  for  experimental  purposes.  This  leads  to  that 
point  of  the  development  which  produced  the  present  furnaces, 
to  be  considered  more  closely  in  later  chapters;  at  this  time, 
therefore,  only  the  historical  facts  will  be  recorded  in  a  general 
way. 

In  1898  Stassano  took  out  a  patent  in  different  countries 
claiming:  "A  method  for  the  practical  production  of  liquid 
wrought  iron  of  any  degree  of  carbon  and  of  liquid  alloys  of  iron 
by  means  of  the  electric  current."  Stassano's  furnace  under- 


HISTORICAL  9 

went  many  constructive  alterations  as  a  result  of  experiments 
made  to  obtain  a  practical  apparatus,  but  his  furnaces  even  as 
used  today  are  based  on  the  old  principle  of  heating. 

The  next  most  important  type  of  furnace  used  today,  the 
Heroult,  appeared  in  the  years  1899  and  1900,  and  almost  at  the 
same  time  Kjellin  with  his  induction  furnace  succeeded  in  pro- 
ducing an  apparatus  of  practical  use  in  the  iron 'industry. 

All  these  three  furnaces  were  operated  by  electricity  generated 
by  .means  of  water-power.  The  Stassano  in  upper  Italy,  the 
Heroult  in  Savoy,  and  the  Kjellin  in  Sweden,  and  their  practical 
success,  first  drew  the  interest  of  the  iron  industry.  An  impor- 
tant contributing  factor  also  was  a  report  by  Dr.  Haanel,  chief 
of  a  commission  of  experts  sent  by  the  Canadian  Government  to 
Europe  to  study  the  electric  furnace. 

This  report  first  brought  together  the  different  existing 
types  of  furnaces  and  considered  them  in  their  relation  to  each 
other.  The  plants  of  Gysinge,  Kortfors,  La  Praz,  Turin,  and 
Livet  were  inspected,  and  it  was  found  that  a  Kjellin  furnace  in 
Gysinge  produced  a  superior  quality  of  steel  from  raw  materials 
consisting  of  charcoal  iron  and  scrap  iron.  In  Kortfors,  and 
also  in  La  Praz,  the  Heroult  steel  process  was  in  operation,  any 
desired  quality  of  steel  being  produced  by  the  method  of  first 
melting  scrap  and  then  refining  it  by  the  use  of  a  large  variety 
of  slags.  The  Stassano  furnace  in  Turin  was  not  in  operation 
at  the  time  of  the  commission's  inspection.  In  Livet  a  furnace 
by  Keller,  of  a  construction  similar  to  that  of  Heroult,  was  busy 
melting  iron  direct  from  the  ore. 

From  the  above  it  is  evident  that  in  1904,  the  time  of  the 
Canadian  Commission's  tour,  the  electro-steel  industry  had  at- 
tained a  healthy  existence,  at  least  where  in  proximity  to  water- 
power  developments.  The  principal  hindrance  to  the  introduc- 
tion of  the  electric  furnace  in  the  iron  industry  had  now  been 
overcome.  In  the  production  of  steel  the  problem  was  to  keep 
the  iron  from  absorbing  the  carbon  of  the  electrodes,  and  both 
Kjellin  and  Heroult  successfully  solved  the  difficulty  although  in 
different  ways.  Kjellin  avoided  the  use  of  electrodes  entirely, 
while  Heroult  brought  the  electric  current  into  the  furnace 


10  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

through  carbon  electrodes,  following  the  method  used  (for  ex- 
ample) in  the  aluminum  industry,  where  the  electrolysis  of  the 
molten  mass  is  desired.  He,  however,  arranged  his  furnace  so 
that  there  always  remained  a  layer  of  slag  interposed  between  the 
metal  and  the  carbon,  thus  avoiding  contact  between  the  two. 

Stassano  sought  to  attain  his  goal  in  the  reduction  of  iron 
directly  from  the  ore  and  only  later  turned  to  the  scrap-iron 
method.  Heroult  and  Kjellin  were  the  first  to  regularly  engage 
in  the  business  of  melting  scrap  iron  in  the  electric  furnace. 
And  again  it  is  Heroult  to  whom  credit  is  due  for  the  develop- 
ment of  the  art,  to  the  end  that  from  a  charge  of  ordinary  scrap 
any  desired  quality  of  steel  may  be  obtained  by  refining  it. 

Improvements  in  the  machinery  for  generating  electric 
currents,  especially  in  the  design  of  gas  engines  of  large  capacity, 
had  in  the  mean  time  opened  the  way  for  other  cheap  methods  of 
producing  electricity,  so  that  the  electro-steel  industry  was  no 
longer  limited  to  water-power  locations.  In  1905  there  appeared 
the  first  such  industry  in  Germany,  in  the  works  of  Richard 
Lindenberg  in  Remscheid.  The  installation  consisted  in  one 
Heroult  furnace. 

In  the  same  year  the  Rochling  Iron  and  Steel  Works  erected 
a  Kjellin  furnace  and  were  the  first  to  try  the  experiment  of 
running  an  electric  furnace  in  conjunction  with  a  great  iron 
establishment. 

There  remains  to  be  mentioned  that  during  this  period  the 
now  much  used  Girod  furnace  appeared  in  a  small  way,  and  that 
the  year  1906  was  marked  by  the  appearance  of  the  Rochling- 
Rodenhauser  furnace,  of  which  the  following  chapters  will 
speak  more  fully.  With  the  latter  there  now  existed  an  induction 
furnace  by  means  of  which  (as  also  with  the  Heroult  furnace) 
a  superior  steel  of  any  desired  quality  could  be  obtained  from  a 
charge  of  any  kind  of  raw  material. 

In  recent  years  successful  efforts  have  been  made  to  produce 
iron  by  means  of  the  electric-shaft  furnace  of  Gronwall,  Lindblad 
&  Stalhane  and  others  in  California.  More  modern  times  have 
arrived  and  in  the  following  chapters  will  be  found  a  discussion  of 
the  present  day  furnaces  as  used  in  the  electric-steel  industry. 


L.  I  EB  R  A  t-t  Y 


CHAI 

Los 


CHAPTER  II 

SOME  FUNDAMENTAL  LAWS  AND  TERMS  OF 
ELECTRICAL  ENGINEERING 

BEFORE  turning  to  a  discussion  of  the  different  types  of 
electric  furnaces  used  today,  it  is  necessary  to  have  a  clear  under- 
standing of  some  of  the  fundamental  electrical  laws  and  terms, 
for  it  is  only  through  a  knowledge  of  this,  that  an  electric  furnace 
can  rightly  be  judged  and  a  correct  picture  conceived  of  the 
occurring  phenomena.  In  order  to  begin  with  the  most  impor- 
tant foundation  for  all  electrical  investigations  we  have  first  to 
deal  with  Ohm's  law.  This  law  says: 

Drop  in  potential 
Current  =  -    p     .  f 

Resistance 

or  if  i  denotes  the  current,  e  the  drop  in  volts  and  r  the  resistance — 


The  resistance  r  of  a  conductor  is  determined  by  the  equation: 

cl 


where  /  denotes  the  length  and  q  the  cross-section  of  the  con- 
ductor, while  c  is  a  constant  depending  upon  the  material. 

It  can  be  shown,  for  instance,  that  under  the  same  electrical 
conditions  and  measurements,  a  copper  conductor  will  convey 
5X  times  the  current  that  an  iron  conductor  will.  The  reason 
underlying  this  is  that  evidently  copper  conducts  electricity 
better  than  iron.  We  therefore  speak  of  the  different  conduc- 
tivities of  different  materials. 

The  above-mentioned  phenomena  may,  however,  be  explained, 
since  different  materials  give  entirely  different  resistances,  even 
though  the  dimensions  may  be  the  same.  The  resistance  factor 
dependent  on  this  material  is  called  the  "specific  resistance" 

11 


12      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

and  is  mathematically  indicated  by  p,  so  that  the  formula  for 
the  resistance  of  a  conductor  is, 

r  =  c  —  and  may  now  be  written  :  r  =  p  — 
q  p  q 

The  different  conductivities  are  consequently  the  reciprocal 
values  of  the  specific  resistances. 

In  order  to  be  able  to  apply  our  first  law,  the  "ohmic  law," 
we  must  clearly  establish  the  electrical  units.  The  current 
quantity  is  measured  in  Amperes,  the  potential  or  pressure  in 
Volts,  and  the  resistance  in  Ohms. 

Originally  the  unit  of  resistance  as  established  by  Siemens 
consisted  of  a  column  of  mercury  one  metre  long  and  of  one 
square  millimetre  cross-section  at  a  temperature  of  o°  centigrade. 
In  place  of  this  resistance  unit,  we  have  the  ohm  to-day,  which 
equals  1.063  Siemens  units  and  corresponds  to  a  mercury  column 
1.063  m.  long,  of  i  sq.  mm.  cross-section  at  o°  C. 

The  generally  applied  resistance  unit,  the  ohm,  was  established 
in  such  a  way  that,  with  a  pressure  of  one  volt,  and  a  resistance 
of  one  ohm,  a  current  of  one  ampere  resulted. 

We  now  know  what  the  dimensions  of  the  mercury  column 
are,  and  under  which  conditions  it  has  a  resistance  of  one  ohm, 
and  since  the  resistance  of  a  conductor  is, 

l_  I  is  in  metres 

r  ~  p  q  W  '  re  q  in  square  millimetres 

we  may  calculate  the  specific  resistance  for  mercury,  which  is 


.. 
i  ohm  =  p  —          —  or  p  =  i  :  1.063  =  -94°73 

In  the  above  description  of  the  resistance  unit  the  temperature 
was  always  given.  This  was  not  done  without  having  an  object 
in  view,  for  the  specific  resistance  of  a  conductor  is  not  only 
dependent  on  the  material,  but  also  on  its  temperature.  There- 
fore, equal  conductors  at  different  temperatures  have  different 
resistances,  and  consequently  with  the  same  voltage  they  carry 
different  currents. 


LAWS   AND   FUNDAMENTAL  PRINCIPLES    OF   ELECTRICITY      13 

The  conditions  governing  the  alterations  of  the  specific 
resistance  with  changing  temperatures  have  been  established, 
by  making  exact  measurements  with  the  different  materials.  In 
a  similar  way  the  specific  resistances  were  determined. 

Concerning  the  changes  in  temperature,  it  was  shown 
that  the  resistance  of  the  metals  and  their  alloys  rose  with 
increasing  temperatures  and  in  accordance  with  the  following 
formula: 


where  r0  =  the  resistance  at  o° 

rt  =  the  resistance  at  t° 

a  and  /3  are  numerical  constants,  which  have  to  be  specially 
determined  for  each  conductor. 

For  practical  purposes  when  within  moderate  temperature 
differences,  it  will  suffice  if  we  use  the  following  formula: 

rt  =  r0  (i  +  a  i) 

It  is  well  known  that  the  specific  resistance  of  a  metal  de- 
pends so  much  on  various  substances  mixed  with  it,  that  accurate 
figures,  as  they  are  known  for  the  absolutely  pure  metal,  have 
practically  only  a  comparatively  small  value.  It  is  sufficient 
therefore  to  figure  practically  with  the  following  values: 

Material  p 

Copper  ........................................  %5 

Brass,  Iron,  Platinum,  Zinc  ......................  ^o 

German  Silver,  and  similar    German  Silver  alloys: 

Monel  metal  ...............................        %  to  % 

Carbon  varies  between  ..........................    100  and  1,000 

The  exact  values  of  the  specific  resistances,  and  the  tempera- 
ture coefficients,  are  given  for  some  of  the  materials  which  are 
used  in  the  construction  of  electric  furnaces.  It  is  to  be  noted 
that  the  temperature  coefficient  for  metals  is  positive,  i.e.,  with 
rising  temperature  its  resistance  increases.  In  contradistinc- 
tion to  this,  carbon  and  non-metallic  conductors  are  negative,  i.e., 
with  rising  temperatures  the  resistance  is  decreased. 


14      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Material 

P  at  15°  C 

a 

03    to    05 

-J-    OOtQ 

Lead                   

22 

+    0041 

Iron  
Copper    

.10     tO   .12 

.018  to  .019 

+  .0045 
+  .OO37 

07    to    08 

-J-    OOI5 

German  Silver  
Nickel  
Platinum  
Silver  

.15    to  .36 

-15 
.12      tO   .16 

.016  to  .018 

+  .  OOO2  to   .  OOO4 
+  .0037 

+  .0024  to  .0035 
+  .  0034  to  .  0040 

Steel 

10    to    25 

+  0052 

Zinc 

06 

+  .0042 

Carbon  

100  tO  1000 

—  .  0003  to  .  0008 

The  temperature  coefficients  in  the  above  table  are  only 
exactly  accurate  within  comparatively  small  temperature  in- 
tervals, in  fact,  are  absolutely  accurate  only  within  the  limits 
of  o  to  30°  C.  This  is  why  the  temperature  coefficient  only 
gives  an  approximate  idea  of  the  increase  in  the  specific  resist- 
ance. For  instance,  that  which  interests  us  the  most  is  iron, 
with  its  growing  temperatures.  Unfortunately  exact  measure- 
ments of  the  resistance  of  iron  at  high  temperatures  are  extremely 
difficult  to  make,  and  this  is  why  we  see  so  many  contradictory 
statements  concerning  these.  It  is  evident  that  the  resistance 
of  solid  and  also  fluid  iron  varies  with  its  chemical  composition. 
To  some  extent  a  certain  portion  of  the  iron  content  will  include 
gases  and  slag  particles  at  the  beginning  of  the  run,  and  this 
causes  it  to  have  a  higher  resistance  than  it  would  have  at  the 
end  of  the  heat,  yet  keeping  the  composition  the  same.  But  all 
of  these  influences  are  practically  negligible;  for  in  the  many 
years'  experience  of  the  author  in  operating  electric  furnaces, 
there  has  never  been  any  significant  or  practically  real  influence 
of  the  refining  which  could  be  credited  to  a  change  in  the  re- 
sistance of  the  iron.  Thus  the  above-mentioned  causes,  which 
could  theoretically  call  forth  a  change  in  the  resistance,  may  be 
neglected  in  practise.  We  may  now  use  the  formulas  and  values 
which  are  sufficiently  correct  for  practical  purposes,  and  which 
are  obtained  by  exact  measurements  for  low  temperatures.  It 


LAWS   AND   FUNDAMENTAL   PRINCIPLES    OF   ELECTRICITY      15 

has  been  established  that  the  specific  resistance  of  ordinary  basic 
bessemer  iron  at  temperatures  from  o°  to  160°  C.,  would  change 
according  to  the  following  formulas: 

Pt  =  .13  (i  +  5  X  io~3/  +  3.6  X  icrV) 

If  in  accordance  with  this  formula  we  figure  the  value  of  pt  for 
1700°,  we  obtain 


This  result  seems  somewhat  too  high,  as  far  as  it  can  be 
judged  with  the  operating  values  on  hand  which  were  obtained 
by  the  author,  who  has  had  the  best  results  when  figuring  with 
a  mean  value  of  p  =  1.66  when  designing  electric  furnaces. 
Gin  figured  according  to  Neumann  with  a  resistance  of  iron 
of  .000175  °nm  Per  cubic  centimetre.  This  would  correspond 
to  a  specific  resistance  of  p  =  1.75.  This  figure  also  shows  that 
the  result  calculated  above  for  the  specific  resistance  of  fluid 
iron  is  too  high  at  2.12.  In  this  book  p  =  1.66  will  always  be 
used  as  the  specific  resistance  of  molten  iron.  Even  though 
this  value  cannot  lay  claim  to  any  theoretical  accuracy,  the 
calculations  will,  however,  give  results  which  correspond 
sufficiently  with  practical  operating  conditions. 

It  was  remarked  upon  before  that  carbon,  in  contradistinc- 
tion to  the  metals,  has  a  negative  temperature  coefficient,  so 
that  with  increasing  temperatures  the  resistance  of  the  carbon 
decreases.  This  phenomenon  we  have,  however,  in  a  much 
more  extraordinary  measure,  with  the  so-called  "conductors  of 
the  second  class."  Under  this  heading  we  mean  materials,  or 
bodies,  which  at  ordinary  temperatures  have  practically  no 
conductivity,  or  at  least  so  small  a  one  as  not  to  be  worthy  of 
consideration.  With  increasing  temperatures  these  conductors 
of  the  second  class  attain  steadily  bettering  conductivities,  so 
that  they  can  eventually  be  used  as  conductors  directly.  We 
shall  have  to  deal  with  conductors  of  the  second  class  in  detail, 
when  discussing  the  various  furnace  types.  It  may  be  well 
here  to  speak  of  the  well-known  application  of  a  conductor  of 
the  second  class,  in  the  form  of  the  filament  or  glower  of  the 


16      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Nernst  lamp,  which  consists  of  porcelain  and  magnesia,  which 
substances  are  non-conductors  at  ordinary  temperatures.  The 
glower  of  the  Nernst  lamp  must  therefore  be  warmed  up  first, 
before  it  is  in  any  way  capable  of  taking  up  the  lighting  current. 
This  pre-heating  was  at  first  accomplished  with  the  heat  of  an 
ordinary  match,  whereas  it  is  to-day  done  electrically.  All 
substances  which  are  used  for  fire-resisting  materials  for  the 
lining  of  electric  furnaces,  are  similar  in  a  way  to  the  filament 
of  a  Nernst  lamp,  i.e.,  all  constructional  material  for  the  hearth 
or  roof  becomes  a  more  or  less  good  conductor,  at  the  high  tem- 
peratures which  are  prevalent  in  electric  furnaces,  and  this  is, 
of  course,  taken  into  consideration  in  their  construction,  as  will 
be  made  evident  later  on. 

The  constructional  material  used  most,  for  the.  lining  of 
electric  furnaces,  is  dolomite  or  magnesite,  aside  from  the  pro- 
tecting brickwork  used  as  a  backing,  and  aside  from  the  roof 
material.  This  material  is  mixed  with  tar  and  pressed  into 
bricks,  which  are  later  on  used  in  the  furnace  hearth,  or  it  is 
directly  tamped  into  the  furnace.  The  furnace  walls  produced 
in  this  way  have  a  small  conductivity  in  their  cold  state,  so  that 
in  such  a  case  they  may  be  regarded  as  non-conductors.  They 
lose  their  resistance  with  increasing  temperatures  very  fast,  as 
is  shown  in  Fig.  9,  which  shows  the  results  of  an  investigation,  in 
graphic  form,  of  the  resistance  measurements  of  magnesite  and 
tar  rods,  in  relation  to  the  temperature.  The  curve  shows 
plainly  how  the  specific  resistance  suddenly  falls.  This  is  desig- 
nated by  p  in  the  figure.  It  also  gives  a  characteristic  picture 
of  the  conductivity  conditions,  as  they  appear  with  conductors 
of  the  second  class.  We  will  recur  to  this  matter  again  in  due 
course. 

As  we  have  already  dealt  with  the  prime  laws  of  all  electrical 
calculations,  we  will  now  deal  briefly  with  the  possibilities  of 
different  connections.  This  leads  us  to  the  series  and  parallel 
connections.  Both  connections  will  again  be  met  in  the  detailed 
description  of  electric  furnaces.  As  both  have  their  advantages 
and  disadvantages,  it  seems  well  that  the  prime  difference  be 
clearly  stated. 


LAWS    AND    FUNDAMENTAL    PRINCIPLES    OF    ELECTRICITY       17 

We  will  therefore  again  recur  to  the  analogy  between  elec- 
tricity and  water.  Let  us  suppose  we  had  a  water-power  of 
very  high  fall  but  of  comparatively  very  little  water,  and  that 
several  water-wheels  were  to  be  driven  with  it.  If  the  wheels 
could  be  operated  at  any  place  it  would  be  best,  with  the  small 


Temperature 


FIG.  9. 

amount  of  water  available,  that  it  be  used  time  and  again,  or 
sausage-like  in  series,  through  the  different  wheels.  That  is  to 
say,  the  water-wheels  could  be  arranged  at  different  elevations 
of  the  fall,  and  thus  by  dividing  the  pressure  an  equal  amount 
of  water  could  be  used  to  drive  each  wheel.  The  small  amount 
of  water  is  similar  to  a  small  current,  the  high  fall  or  great  differ- 
ence in  pressure  is  similar  to  a  high  voltage.  In  such  a  case  if 
the  current  present  can  be  used  in  the  electric  apparatus  installed, 
but  only  a  portion  of  the  prevalent  voltage  is  required,  then  the 
apparatus  utilizing  the  current  can  be  so  made,  that  it  only 
absorbs  a  portion  of  the  voltage.  In  this  case,  therefore,  the  same 
current  and  same  amperage  flows  through  the  various  apparatus 
using  it,  and  we  consequently  speak  of  a  ''series  connection." 


18      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

We  may,  however,  also  conceive  of  a  case  where  a  water-fall 
consists  of  a  considerable  quantity  of  water,  but  has  only  a  small 
pressure.  A  well-known  case  is  on  the  Mississippi  River  at 
Keokuk,  where  eventually  230,000  HP,  at  25  cycles,  3-phase 
current  will  be  generated.  Here  it  would  be  practically  im- 
possible to  use  this  immense  volume  of  water  in  one  turbine. 
We  are  therefore  obliged  to  separate  these  large  volumes  of  water 
where  each  part  materially  has  the  same  fall,  between  the  intake 
and  the  tail-race.  We  have  here  then  a  case  where  several 
turbines  are  arranged  next  to  each  other.  This  case  also  has 
its  simile  in  electrical  engineering,  the  best  known  case  being 
perhaps  the  ordinary  incandescent  lamp,  where  the  circuit  is 
also  so  arranged  that  only  a  small  part  of  the  main  current 
flows  through  each  lamp,  at  the  same  voltage  for  each.  There 
may  be  any  number  of  lamps  next  to  each  other,  or  as  we  say, 
they  receive  their  current  in  parallel. 

Both  cases  are  used  in  electric-furnace  constructions.  The 
Heroult  furnace  is  an  example  of  a  series  connection,  while  the 
Girod  furnace  employs  a  parallel  connection. 

These  furnaces  are  described  later  on,  but  a  few  words  here 
concerning  their  method  of  connections  will  not  be  amiss. 
Figure  10  shows  the  schematic  wiring  diagram  of  a  Heroult 
furnace,  while  Fig.  n  shows  the  main  features  of  the  connection 
in  a  Girod  furnace.  It  is  evident,  that  in  Fig.  10,  the  current 
would  flow  through  first  one  and  then  the  other  conductor, 
whereas  in  Fig.  n  the  two  points  of  the  circuit  are  connected 
together  by  means  of  two  conductors  connected  iri  parallel.  Of 
course  Ohm's  law  is  applicable  in  both  cases.  Accordingly  with 
a  resistance  of  r  in  the  conductor  and  having  a  voltage  e  between 

its  terminals,  we  would  have  a  current  of  i  =  —  amperes.     If 

the  voltage  e,  in  Fig.  n,  is  prevalent  between  the  points  A  and 
B,  Ohm's  law  will,  of  course,  hold  for  each  parallel  connected 
conductor. 

Suppose  that  between  the  points  A  and  B,  we  have  the 
voltage  e  and  between  these  points  we  also  have  the  resistances 
r\  and  r2,  the  resultant  current  being  ii  and  i2,  respectively. 


LAWS   AND    FUNDAMENTAL   PRINCIPLES    OF    ELECTRICITY      19 


Then  in  a  similar  way  as  with  the  water-wheels,  the  main  current 
will  be  equal  to  the  sum  of  its  parts,  i.e.,  i  =  ii  +  i».  We  there- 
fore have  the  first  of  Kirchhoffs  laws:  "At  each  point  of 
division  the  sum  of  all  the  incoming  currents  equals  the  sum  of  all 
the  outgoing  currents,  or  at  each  point  of  division  the  sum  of  all 
currents  equals  zero."  With  this  it  is  assumed  that  the  incoming 
currents  are  regarded  as  positive  and  the  outgoing  as  negative 
currents. 


r 


FIG.  10. 


FIG.  ii. 


From  Fig.  1  1  it  follows  that,  ii  =  —  and  i2  =  —  or  e 

r\  rz 


i  r\ 


and  e  =  iz  rz.  From  this  it  follows  that  i\  X  r\  =  i%  X  rz  or  we 
have  the  proportion  i\  :  iz  ::  rz  :  r\,  i.e.,  currents  which  flow 
parallel  to  each  other  vary  inversely  as  the  resistances  of  the  parallel 
connected  conductors." 

We  will  now  investigate  how  large  the  combined  resistance 
becomes,  i.e.,  the  resistance  which  is  there,  when  both  the 
parallel  connected  conductors  r{  and  rz  are  opposed  to  the  current 
flowing. 

In  order  to  answer  this  question,  suppose  the  two  parallel 
connected  conductors  to  be  replaced  by  a  single  conductor, 
having  the  same  combined  resistance  r.  This  would  not  change 


20      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  current  conditions,  and  with  the  voltage  e  between  A  and  B 
remaining  the  same,  we  would  also  have  the  total  current  * 

remaining,  so  that,  i  =  —  as  before. 

As  demonstrated  before  i  =  i\  -f  2*2  •  If  we  substitute  for 
these  current  volumes  their  corresponding  voltage  and  resist- 
ance equivalents  we  have: 


666  III 

consequently  —  = 1 or  —  = 1 

J    r       r,       r2        r        ri       r2 


This  gives  the  size  of  the  combined  resistance. 

=  ri  x  rz 
r\  +  rz 

In  the  same  way  this  rule  also  holds  for  n  parallel  connected 
circuits.  Designating  the  combined  resistances  again  by  r,  we 
have, 

JL  ,  i  +  i  +  i  +  .      .  -L 

r        ri        rz        r3  n 

As  the  reciprocal  of  the  resistance  is  designated  as  the  conduc- 
tivity, we  may  define  this  equation  by: 

"  The  conductivity  of  a  combination  of  conductors  is  equal  to 
the  sum  of  the  conductivities  of  the  single  conductors.1' 

If  the  n  conductors  are  equal  to  each  other,  then 

11,1,1,  i         n  ri 

—  = i 1 1-....-! =  —  or    r  =  — 

r        ri        TI        ri  ri        n  n 

i.e.,  "The  combined  resistance,  of  n  parallel  connected  resist- 
ances, equal  to  each  other,  is  equal  to  the  nth  part  of  any  single 
resistance" 

In  accordance  with  the  above,  it  is  now  possible  to  give  an 
arithmetical  example  of  electric-circuit  conditions,  as  they  are 
often  found  with  electric  furnaces. 


LAWS    AND    FUNDAMENTAL   PRINCIPLES    OF    ELECTRICITY      21 


The  circuit  is  to  consist  of  two  carbon  blocks  or  electrodes 
in  touch  with  a  connecting  iron  block.  The  carbons  and  the  iron 
may  have  equal  cross-sections,  and  may  be  round  of,  say,  350  mm. 
diameter  (about  14  inches).  The  length  of  each  carbon  block 
is  to  be  1.5  metres  (about  60  inches),  and  the  length  of  the  iron 
block  i  metre  (about  40  inches). 

In  calculating  the  resistance  of  each  part  of  the  circuit  we 

know  that  r  =  p  X  —  .     In  glancing  at  Fig.  12,  we  may  take  the 

circuit  as  consisting  of  two  equal  parts,  which  are  connected  in 
series  in  the  first  place,  and  in  parallel  in  the  second  case.  The 
resistance  r'  ',  as  shown  by  the  figure,  is  composed  of  the  resist- 
ance rc  of  the  carbon  block,  and  the  resistance  rFe  or  half  of  the 
iron  block. 

Consequently, 

rc  =  PC  -£  =  5°o^T  =  -00779  ohm. 

(Here  the  average  value  for  pc  is  taken  from 
the  table  on  page  14,  where  the  specific  resis- 
tances of  carbon  are  given.) 

lpe  .  SO 

rPe  =  pFe  —  =  .11  -  27"  =.000000572  ohm. 


-  27" 

35°  — 


Fio 


Here  the  average  value  for  pFe  was  also  taken 
from  the  table. 

Even    this    short    example    shows    how  very 
small    the  iron  resistance  is   compared  with  the 
carbon.          For     even     were     the     carbon    and 
iron,  in  the  above  example,  of  equal  lengths,  the  iron  resis- 
tance value  would  have  risen  to  three  times  the  value  given 

(  =  —  —  ),  but  even  so  the  carbon  would  still  have  a  resistance 
V      .5oo/' 

2,500  times  as  great  as  that  of  iron,  and  this  is  entirely  on  account 
of  the  extraordinary  differences  in  their  specific  resistances. 

Turning  again  to  the  example,  we  find  that  we  know  the  re- 
sistance of  the  parts  of  which  the  circuit  is  composed.    It  is 
r'  =  rc  +  rFe  =  .007790572  ohm. 


22      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

In  case  of  a  series  connection  the  current  would  have  to 
traverse  this  resistance  twice,  so  that  this  resistance  would  be, 

rH  =  2  r'  =  2  X  .00779  =  -OI558  ohm. 
In  the  second  case,  i.e.,  with  a  parallel  connection,  we  have  a 
total  resistance  composed  of  a  combined  resistance,  consisting 
of  two  similarly  constituted  parts,  each  having  a  resistance  of 

r'  =  rc  +  rFc  =  .007790572  ohm. 

As  the  combination  resistances  are  alike  and  in  parallel,  we 
have  n  =  2  for  the  above  case,  or 

rp  =  —  =  .003895  +  ohm. 

It  is  evident,  therefore,  with  the  same  conductor  under 
the  same  conditions,  but  in  the  first  case  having  been  in  series, 
and  in  the  other  case  connected  in  parallel,  that  the  series 
connection  has  four  times  the  resistance  of  the  parallel  con- 
nection. 

This  extraordinarily  different  resistance  of  the  two  connections 
is,  of  course,  not  without  its  influence  on  the  current  and  voltage 

conditions.    This  is  evident  from  Ohm's  law,  where  i  =  —  and 

the  example  before  us  with  equal  voltages  gives  us  four  times 
the  current  with  the  parallel  connection,  as  it  does  with  the  series 
connection.  Or  as  e  =  i  r,  and  if  we  wanted  equal  currents  in 
both  cases,  we  would  have  to  have  four  times  the  voltage  in  the 
case  of  the  series  connections,  compared  to  the  parallel  arrange- 
ment of  conductors. 

It  may  be  well  to  mention  here,  that  the  above  example 
only  holds  for  arc  furnaces,  with  series  or  parallel  connected 
electrodes,  when  the  electrode  measurements  are  alike,  as  they 
were  assumed  to  be  in  the  example. 

What  action  is  there  then,  when  an  electric  current  flows  through 
a  conductor?  It  has  always  been  evident  in  order  that  the 
current  may  flow  through  a  conductor  that  a  definite  voltage 
was  necessary,  in  order  to  overcome  the  resistance.  Consequent- 
ly, when  an  electric  current  flows  through  any  conductor  a 


LAWS    AND    FUNDAMENTAL    PRINCIPLES    OF    ELECTRICITY      23 

certain  work  fe  accomplished,  which  must  come  to  the  surface  in 
one  form  or  another.  In  our  case,  we  find  work  produced  by 
the  current,  showing  in  the  conductor  again  as  heat.  In  what 
degree  this  heat  is  developed,  is  given  us  by  Joule's  law.  This 
was  established  by  the  English  physicist  Joule,  and  experiment- 
ally determined  by  him.  It  is  as  follows: 

"  The  heat  developed  by  a  current  flowing  through  a  conductor, 
is  directly  proportional  to  the  time,  proportional  to  the  resistance 
and  proportional  to  the  square  of  the  current,"  or  Q  =  C  i?  rt, 
where 

Q  =  the  heat  generated 

/  =  the  time  the  current  is  flowing 

i  =  strength  of  the  current 

r  =  the  resistance 
and  C  =  a  constant  dependent  on  the  units  chosen. 

If  the  current  i  is  measured  in  amperes,  the  potential  e  in 
volts  and  the  time  /  in  seconds,  then  C  =  .24,  which  has  been 
determined  by  most  accurate  measurements.  Therefore 

Q  =  .24  ?r  t  gram  calories  or,  as  according  to  Ohm's  law 
e  =  ir,  we  have  • 
Q  =  .24  eit  gram  calories. 

If  the  heat  is  to  be  measured  in  kilogram  calories,  it  is  to  be 
noted  that  i  Kg.  calorie  =  1000  gram  calories,  so  that  the  right 
side  of  our  equation  is  to  be  divided  by  1000. 

If  the  work  produced  is  not  to  be  expressed  in  kilogram 
calories,  but  in  metre  kilograms  (or  the  equivalent  of  the  foot  lb.), 
we  find  that  i  Kg.  calorie  =  424.7  metre  kilograms.  If  the 
work  delivered  be  designated  by  A ,  we  have 

.24  eit 
A  =  424.7  =  .1019  eit  m.  kg. 

now. 1019  = —  —  i.e.,  it  is  equal  to  the  reciprocal  of  accelera- 
9.0! 

tion,  consequently 

A  =  —    —  metre  kilograms. 


24  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

We  usually  denote  the  work  delivered  in  one  second  as  effect  or 
power,  and  have  chosen  p  to  denote  it,  hence, 

eit 
p  =  — -JT-  metre  kilograms. 

With  electrical  measurements  we  do  not  desire  to  determine 
the  effect  in  kilogram  metres,  but  in  volts  X  ampers,  or  in  short 
voltampers,  otherwise  known  as  watts,  while  the  work  in  joules  = 
.24  eit,  or  as  eit  is  measured  in  watt-seconds,  watt-hours  or  kilo- 
watt-hours, all  in  accordance  with  the  measurement  of  time, 
be  it  in  seconds  or  hours,  and  whether  the  power  is  to  be 
inserted  in  watts  or  kilowatts.  Thereby  i  kilowatt  =  1000 
watts. 

For  the  conversion  of  metric  horse-power  into  watts,  the 
lollowing  are  determining  factors: 

i  HP  metric  =  75  kg.  m.;   as  the  electric  power 

e  i    . 
p  = — ^-  m  kg.  =  ei  watt 

i.e.,  i  m.  kg.  =  9.81  watt,  consequently  i  HP  =  75  m.  kg. 
=  75  X  9.81  watt  =  736  watts.1 

This  gives  the  relation  between  the  mechanical  and  electrical 
units.  If  we  arrange  the  determined  factors  in  the  form  of 
a  table,  we  obtain  the  following: 

The  heat  generated  in  a  conductor  by  a  current  is, 
Q  =  .24  eit  gram  calories 
=  .24  i~  rt  gram  calories 
where  e  is  to  be  inserted  in  volts 
i  is  in  amperes 
r  is  in  ohms 
/  is  in  seconds. 

The  power,  or  the  effect  is 

p  =   ei  watt  or  volt  amperes 
=  i2  r  watt. 

^ne  British  HP  =  33,000  ft.  Ib.  per  minute  =  746  watts. 


LAWS   AND   FUNDAMENTAL   PRINCIPLES   OF   ELECTRICITY      25 

Here         "  i  kilowatt  =  1000  watts 


i     m.  kg. 
i  m.  kg.  =  9.806  watt  =  - 


i  HP  =  736  watts  =  75 


75  seconds 
m.  kg. 


seconds 


The  delivered  work  is  given  by  the  formula, 
A  =  eit  watt-seconds  or  joules 

=  r  rt  watt-seconds  or  joules 
Here  i  watt-second  =  .24  gram  calories  =  i  joule 

=  . 10198  m.  kg. 
i  watt-hour  =  3600  joules  =  864.5  gram  calories 

=  367.1  m.  kg. 
i  kilowatt-hour         =  1000  watt-hours 

=  864.5  kilogram  calories 
=  367ii4m.  kg. 

i  m.  kg.  =  2.35  gram  calories 

=  9.806  watt-seconds. 


CHAPTER  III 
EFFECTS   OF  THE  ELECTRIC   CURRENT 

THE  effects  of  the  electric  current  which  interest  us  most, 
are  its  heating  effects.  Let  us  therefore  consider  what  possi- 
bilities electrical  engineering  offers  for  the  production  of  heat. 

i.  DIRECT  HEATING  BY  RESISTANCE 

In  the  foregoing  chapter  we  have  seen  that  when  an  electric 
current  flows  through  a  conductor,  heat  is  developed  and  the 
quantity  produced  is 

Q  =  .24  eit  gram  calories 

=  .24  •?  rt  gram  calories. 

If  we  for  example  force  an  electric  current  through  an  iron 
conductor  the  temperature  of  this  conductor  will  increase.  The 
heating  will  therefore  be  greater  and  more  rapid  with  increasing 
current  and  increasing  resistance  of  the  iron  conductor.  Possible 
methods  for  making  this  resistance  larger  become  evident  from 
a  glance  at  the  formula  recently  mentioned  which  reads: 

I 

r=^. 
An  increase  of  resistance  occurs  if  the  cross-section  is  reduced, 

or  if  the  length  of  the  iron  conductor  or  the  liquid  metal  bath  is 
increased. 

The  method  of  heating  thus  explained  may  be  called  direct 
heating  by  resistance  for  the  heating  is  affected  solely  by  the 
inherent  resistance  of  the  metal  to  be  heated. 

The  Taussig  furnace,  mentioned  in  Chapter  I,  is  an  example 
of  an  electric  furnace  built  on  this  principle. 

When  we  consider  that  the  direct  heat  by  resistance  is  not 
confined  to  the  metal  it  is  desired  to  heat  and  that  any  such 
method  of  heating  must  also  naturally  cause  heat  to  appear  in 
every  wire  used  to  conduct  the  electric  current,  we  encounter 
the  first  difficulty  which  operates  against  a  practical  utilization 

26 


EFFECTS   OF   THE   ELECTRIC   CURRENT 


27 


of  the  direct  heat  by  resistance  for  the  purpose  of  heating  metal 
baths.     An  iron  bath  is  a  comparatively  favorable  condition  at 

that,  for  the  resistance  being  r  —  p  —  the  specific  resistance  p  is 

of  considerable  importance  in  creating  the  higher  degree  of  heat. 
This  point  is,  of  course,  carefully  considered  in  electrical  engineer- 
ing and  it  is  for  this  reason  primarily  that  copper  is  used  for 
electrical  circuits.  Copper  by  virtue  of  its  small  specific  resistance 
(p  =  .018  to  .019)  is  one  of  the  best  conductors  for  the  transmis- 
sion of  heavy  currents,  for  it  permits  the  use  of  relatively  small 
cross-sections  without  attaining  too 
high  a  temperature.  In  contrast 
thereto  the  specific  resistance  of  iron, 
for  example  (p  =  .1  to  .12),  would  be 
the  deciding  factor -from  the  stand- 
point of  heat  loss,  and  with  equal 
cross-sections  for  copper  and  iron  we 
would  have  a  greater  heat  in  the 
latter  in  the  proportion  of  .1  to 
.018. 

With  equal  cross-sections  for  iron 
and  copper,  and  equal  lengths  of  the 
conductors,  iron  will  attain  a  consid- 
erably higher  temperature.  Espe- 
cially as  its  heat  will  be  further 
increased  by  the  fact  that  the  metal 
in  the  heat  protective  covering  of  the 
electric  furnace  will  rise  to  higher 
temperatures  by  reason  of  its  posi- 
tive heat  coefficient,  which  in  turn 
adds  to  its  resistance.  Yet  the  fact 


FIG.  13. 


FIG.  14. 


FIG.  15. 


still  remains  that  the  specific  resistance  of  iron  must  be  placed  as 
being  very  low.  With  a  system  of  pure  resistance  heating  and 
with  a  resistor  of  iron,  exceedingly  high  current  strengths  would 
be  required  to  produce  the  temperatures  needed  in  electric  fur- 
naces, and  the  currents  would  have  to  be  exceedingly  strong  even 
if  the  cross-section  of  its  iron  resistor  should  be  made  very  great 


28      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

and  the  furnace  bath  cross-section  very  small  in  order  to 
increase  the  resistance  as  much  as  possible. 

An  example  will  serve  to  illustrate  more  clearly  the  condi- 
tions of  this  kind  of  electric  furnace  employing  direct  heat 
resistance. 

Suppose  we  assume  that  by  means  of  pure  resistance  heating, 
a  fluid  iron  bath  of  one  ton  is  to  be  supplied  with  200  kw.  In 
this  case  the  heat  would  be  generated  only  by  the  current  over- 
coming the  resistance  of  the  bath.  This  is  the  amount  of  energy 
with  which  an  electric  furnace  of  i-ton  capacity  would  normally 
be  operated.  In  order  to  make  the  iron  bath  of  as  large  a 
resistance  as  possible,  the  molten  iron  is  to  be  contained  in  a 
long  channel  of  the  smallest  practicable  cross-section.  A  furnace 
of  this  kind  having  a  long  narrow  channel  has  also  been  patented 
by  Gin.  Figs.  13,  14  and  15  show  views  of  this  furnace,  re- 
spectively longitudinal  cross-section,  vertical  cross-section  and 
a  plan  view.  We  might  use  this  arrangement  as  an  example. 
The  size  of  cross-section  has  been  taken  as  10  cm.  (4  inches) 
high  and  5  cm.  (2  inches)  wide.  This  has  been  done  in  order 
not  to  reduce  the  channel  cross-section  to  such  a  degree,  that 
the  furnace  would  be  rendered  inoperative.  Or  if  the  cross- 
section  were  made  much  smaller,  the  cooling  surface  would 
become  extraordinarily  large,  and  thus  cause  very  large  losses. 
This  would  be  entirely  independent  of  the  metallurgical  difficul- 
ties which  would  ensue  if  any  slagging  work  were  attempted  in 
the  narrow  channels.  The  size  channel  chosen  therefore  would 
still  be  practically  workable. 

The  following  assumptions  are  therefore  made  for  this 
example : 

Capacity  of  furnace I  ton  =  (1,000  Kg.) 

Energy  consumption A  =      200  kw. 

Cross-section  of  bath q  =   5,000  sq.  m.m. 

Specific  gravity  of  molten  iron,  about 7.0 

Specific  resistance  p  of  molten  iron,  about 1 .66 

From  this  it.  follows  that: 

Volume  of  iron  =  -     -  =  142.8  cu.  decimetres. 


EFFECTS  OF  THE  ELECTRIC  CURRENT 


29 


142 


-  =  285.6  d.c.m.  =  28.5 


Length  of  the  iron  column  L 
metres  =  about  94  ft. 

Hence  the  resistance  would  be: 

r  =  p  X  —  =  1.66  X  — —  =  .00946  ohm. 

As  the  Joule  effect  A  =  r  r,  we  have 
~A 


It  is  evident  therefore  that  a  very  considerable  current  would 
have  to  be  supplied.  This  also  means  large  copper  cables  for 
bringing  the  current  to  the  furnace,  as  those  of  inadequate  cross- 
section  would  heat  up  too  much. 

The  following  table  shows  the  currents  usually  permitted 
in  wires  and  cables: 


AREA 

CARRYING  CAPACITIES 

Circular  Mils.  (d») 
i  Mil.  =  .oor  Inch 

Square  Mils. 
(d*x.7854) 

Rubber  Insulations 
Amperes 

Other  Insulations 
Amperes 

4106. 

3225. 

12. 

16. 

6529. 

5128. 

17- 

23- 

10381. 

8153- 

24. 

33- 

16509. 

12960. 

33- 

46. 

26250. 

20617. 

46. 

65- 

41742. 

32784. 

65- 

92. 

66373. 

52130. 

90. 

131. 

83694. 

65733. 

107. 

156. 

105538. 

82887. 

127. 

I85. 

I33079. 

104520. 

150. 

220. 

167805. 

I3I790. 

177- 

262. 

2II600. 

166190. 

210. 

312. 

250000. 

196000. 

275- 

412. 

4OOOOO. 

313900. 

330. 

500. 

500000. 

392000. 

390- 

590. 

600000. 

47IOOO. 

450. 

680. 

700000. 

549500. 

500. 

760. 

800000. 

628000. 

550. 

840. 

1000000. 

785400. 

650. 

IOOO. 

30      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  above  table  is  for  insulated  wires,  whereas  bare  conduct- 
ors may  carry  higher  current  densities. 

If  in  the  previous  example  for  the  i-ton  furnace  we  allow 
a  current  density  of  1.5  amperes  per  square  millimetre  (about 
1000  amperes  per  sq.  inch),  the  secondary  conductors  leading 
directly  to  the  furnace  would  have  a  cross-section  of 

=  3065  sq.  mm.  (about  4.75  sq.  inches). 

This  would  entail  .3065  X  10  X  8.9  =  27.28  kg.  of  copper  per 
meter  length  (or  about  19.5  Ibs.  per  foot  length). 

Even  this  value  shows  that  the  leads  for  furnaces  of  the 
simple  resistance  type  become  extraordinarily  expensive,  and  this 
is  especially  so  for  furnaces  of  larger  capacities. 

The  voltage  necessary  to  force  the  required  current  through 
the  iron  bath  of  the  i-ton  furnace  is 

e  =  ir  =  4598  X  .00946  =  43.5  volts. 

These  give  us  the  entire  range  of  electrical  conditions,  but 
these  must  be  considered  primarily  for  direct  current.  When 
operating  electric  furnaces  for  alternating  current,  there  would 
be  certain  deviations,  which  will  not  be  taken  into  consideration, 
as  direct  current  gives  simpler  equations,  so  that  the  above 
calculations  are  quite  sufficient  for  the  case  before  us. 

Considering  the  above  circumstances,  we  may  now  establish 
the  following: 

Characteristic  marks  of  electric  furnaces  having  direct  resistance 
heating. 

a.  Concerning  the  Electric  Characteristics 

As  the  heating  occurs  by  means  of  the  current  passing 
through,  and  overcoming  the  resistance  of  the  iron  bath,  it  is 
entirely  uniform  at  all  places. 

Furthermore  as  the  heat  generated  is  proportional  to  the 
square  of  the  current,  the  smallest  changes  in  the  temperature 
may  be  brought  about  by  altering  the  voltage  of  the  furnace. 
Such  changes  would  be  absolutely  uniform  throughout  the 
entire  bath.  In  this  way  by  choosing  high  enough  voltages,  the 


EFFECTS   OF   THE   ELECTRIC  CURRENT  31 

highest  temperature  may  be  reached.  Besides  this  the  following 
may  be  noted : 

As  the  iron  has  a  comparatively  low  specific  resistance  only 
at  the  high  temperatures  prevalent  in  liquid  iron  baths,  it  follows 
that  direct  resistance  heating  may  only  be  accomplished  by 
applying  very  heavy  currents.  For  the  same  reason  the  voltages 
required  for  the  operation  of  these  furnaces  are  comparatively 
low. 

The  high  currents  have  the  disadvantage  of  demanding 
expensive  cable  installations,  whereas  the  low  voltage  has  the 
advantage  of  simpler  and  easier  insulation,  and  the  advantage 
of  eliminating  all  danger  which  might  befall  the  furnace  attend- 
ants. 

The  high  currents  can  only  be  decreased  by  correspondingly 
increasing  the  voltage  and  contracting  the  bath  cross-section, 
or  by  increasing  the  length  of  the  bath. 

This  brings  us  to: 

b.  The  Metallurgical  Characteristics 

Primarily  the  good  points  here  are  the  uniform  heating,  and 
the  easy  regulation  within  narrow  limits  at  any  desired  high 
temperature. 

The  disadvantages  are : 

To  obtain  good  electrical  conditions  it  is  necessary  to  use 
long  channels  having  small  cross-section  which  means  large 
coob'ng  surfaces.  This  is  equivalent  to  high  thermal  losses 
which  must  be  covered  by  expensive  electrical  energy — con- 
sequently making  the  power-consumption  figures  very  high. 

It  seems  that  a  regular  operation  of  metallurgical  process  is 
precluded,  as  the  working  with  slag  and  moreover  the  changing 
of  slag  would  almost  offer  practically  unsurmountable  obstacles 
in  the  line  channels.  A  uniform  composition  of  the  furnace 
contents  would  hence  be  unattainable.  A  lasting  durability  of 
the  furnace  refractories  also  seems  practically  unobtainable, 
considering  that  the  refractory  walls  between  the  channels  are 
attacked  from  both  sides  by  molten  iron. 

This  direct  resistance  furnace,  with  its  channels  running  to 


32   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

and  fro,  still  fails  in  spite  of  several  electrical  advantages.  Prac- 
tical operation  has  also  shown  this.  For  the  one  furnace  of 
Gin  built  as  here  described,  was  an  utter  failure.  Even  so, 
we  see  patent  applications  today  of  similar  ideas,  which  are 
to  be  discarded,  as  they  are  bound  to  be  unsuccessful  owing  to 
the  same  inherent  weaknesses. 

These  direct  resistance  furnaces,  as  just  described  can  there- 
fore not  be  considered  for  practical  operation  in  the  iron  and 
steel  industry. 

2.  INDUCTION  HEATING 

If  we  are  able  to  circumvent  the  difficulties  of  leading  very 
heavy  currents  to  the  iron  bath,  we  may  decrease  the  resistance 
of  the  bath  at  will  if  we  can  only  increase  the  current  strength 
to  correspond.  This  would  then  allow  us  to  use  furnaces  with 
large  and  wide  hearths  such  as  the  metallurgist  must  necessarily 
demand. 

The  solution  of  the  problem  is  found  in  the  furnace  type 
known  as  induction  furnaces,  which  may  also  be  called  furnaces 
with  resistance  heating.  These  have  the  good  points  of  resist- 
ance heating  with  the  current  being  caused  by  induction,  without 
bringing  with  them  the  disadvantage,  just  mentioned  above,  of 
the  current  having  to  be  led  to  the  furnace  with  immense  con- 
ductors. This  is  what  has  enabled  these  furnaces  to  attain 
their  great  practical  importance. 

On  this  account  induction  furnaces  are  discussed  at  length 
in  the  tenth  and  following  chapters.  It  suffices  to  say  here, 
that  the  induction  furnace  belongs  to  that  group  having  a  type 
of  direct  resistance  heating. 

3.  INDIRECT  RESISTANCE  HEATING 

We  shall  designate  all  furnaces  as  resistance  furnaces  with 
indirect  heating  in  which  the  iron  itself  is  not  the  important 
resisting  element  but  rather  some  other  conductor  of  very  low 
conductivity. 

This  conductor,  that  is  the  actual  heat  resisting  element,  is 
placed  into  the  circuit  and  heated  so  that  it  can  give  up  the  heat 
generated  in  it,  to  the  material  to  be  heated. 


EFFECTS   OF   THE   ELECTRIC   CURRENT 


33 


FIG.  16. 


As  we  can  now  choose  for  the  heat  resisting  body,  a  material 
having  a  very  high  specific  resistance,  the  extremely  heavy 
currents  are  no  longer  required,  which  were  necessary  for  the 
direct  resistance  heating  of  molten  iron.  Consequently  cable 
installation  will  be  less  expensive. 

Such  furnaces  with  indirect  heating  are  often  used  in  labora- 
tories. We  have  for  instance  the  type  suggested  by  Borch- 
ers.  (See  Fig.  16.)  This  has  carbon  blocks  or  rods  of  large 
cross-section  which  serve  as  terminals  between  which  a  carbon 
rod  of  very  small  cross-section  is  clamped,  which  serves  as  the 
heating  resistance  or  resistor.  The  material  to  be  heated  is 
heaped  about  the  small  carbon 
rod.  Thus  while  the  current  is 
flowing,  the  carbon  rod  heats  the 
desired  material  indirectly. 

In  practice  we  find  furnaces 
with  similar  indirect  heating,  but 
they   are    used    mainly   for   the 
manufacture     of     Carborundum. 
Here  we  find  that  a  tamped- 
in  mass  of  powdered  coke  acts 
as  the  heat  resisting  material. 

Such  designs  are  not  used 
in  the  practical  manufacture 
of  iron,  where  the  charge  to 
be  heated  comes  in  direct  con- 
tact with  the  heating  element, 
where  the  latter  is  usually  of 
carbon.  For  it  is  well  known  that  iron  absorbs  carbon  readily 
until  it  is  finally  saturated  with  it.  It  is  consequently  impossi- 
ble to  use  carbon  as  the  heating  element,  not  only  because 
the  carbon  brings  impurities  to  the  iron,  but  primarily  because 
the  carbon  resistance  would  be  worn  away  in  the  shortest  time 
by  the  iron.  In  place  .of  carbon  we  could  suggest  the 
utilization  of  a  conductor  of  the  second  class  as  the  heating 
element.  This  could  be  of  the  same  material  as  the  fur- 
nace lining  which  surrounds  the  metal  bath;  such  as  dolomite 


FIG.  17. 


34    ELECTRIC   FURNACES   IN   THE   IRON   AND    STEEL   INDUSTRY 

or  magnesite  held  together  with  8  to  10  per  cent,  anhydrous 
tar  as  binding  material. 

If  we  were  to  place  such  a  heating  element  or  resistor  in  an 
iron  bath  we  would  have  two  parallel  circuits  for  the  current. 
In  this  case  a  very  poor  conductor  (the  heating  element)  of  very 
high  resistance  would  be  in  parallel  with  a  very  good  conductor 
of  very  low  resistance  (the  iron).  As  the  currents  in  parallel 
circuits  are  inversely  proportional  to  the  resistances  practically 
all  of  the  current  would  flow  through  the  iron  while  the  con- 
ductor of  the  second  class  would  almost  be  without  current. 

Hence  it  is  established  that  it  is  impracticable  for  any  iron 
process  for  furnaces  having  indirect  resistance  heating  to  have  the 
heating  element  in  parallel  with  the  iron  to  be  heated. 

Another  possibility  of  indirect  heating  could  be  obtained  by 
utilizing  the  walls  of  a  vessel,  such  as  a  crucible,  by  heating  it 
with  an  electric  current  either  directly  or  indirectly.  One  of 
the  best  known  of  these  furnace  types  is  the  Hera'us  laboratory 
furnace,  where  the  heating  chamber  is  composed  of  a  cylindrical 
tube,  into  which  small  crucibles  may  be  placed.  The  tube  of 
refractory  material  is  wound  with  a  spiral  of  platinum  wire  or 
ribbon,  which  is  placed  in  the  electrical  circuit,  and  thus  its  heat 
is  transmitted  to  the  furnace  chamber. 

Similar  methods,  however,  have  been  proposed  for  several 
iron  processes,  one  of  these  being  by  Girod.  Accordingly  several 
crucibles  were  placed  in  retorts  composed  of  fire-brick,  the 
bottoms  of  which  were  composed  of  suitable  resistances,  as 
shown  by  Fig.  17.  In  order  not  to  imperil  the  retort  walls  by 
the  heat,  various  resistances  were  used  for  the  bottom  material. 
The  resistance  material  itself  consisted  of  carbon  and  silica. 
With  a  furnace  of  this  kind  utilizing  indirect  heating,  a  tempera- 
ture of  1400  to  1700°  C.  was  reached.  When  the  cross-section 
of  the  heating  element  was  reduced,  as  shown  in  the  sketch, 
temperatures  as  high  as  2000°  C.  were  attained. 

In  these  furnaces,  which  Girod  used  principally  for  making 
ferro-alloys,  he  also  melted  steel.  This  necessitated  IAAO  Kw.- 
hrs.  per  ton  melted. 

In  the  above  we  have  an  electric  furnace  which  differs  only 


EFFECTS   OF   THE   ELECTRIC  CURRENT 


35 


from  the  ordinary  crucible  by  the  electrical  heating.  Even  if 
these  have  several  advantages,  the  Girod  crucible  furnace  still 
has  the  disadvantages  of  the  small  size  of  the  common  crucible, 
the  difficulty  of  obtaining  a  complete  uniformity  from  a  greater 
number  of  crucibles,  the  high  cost  of  the  crucibles,  and.  compared 
to  other  furnaces,  a  very  high  power  consumption. 

All  these  are  reasons  why  these  furnaces  have  not  found  a 
place  in  the  iron  industries.  This  furnace  construction  had  to 
be  mentioned  here,  in  order  to  give  as  complete  a  picture  as 
possible  of  the  various  electrical  heating  possibilities. 


FIG.  18. 


FIG.  i8n. 


We  still  have  to  mention  another  indirect  heating  method, 
where  the  walls  of  the  heating  chamber  are  the  heating  elements 
themselves,  and  consequently  carry  the  current.  One  of  these 
designs  is  the  Helberger  furnace.  This  consists,  as  Fig.  18 
shows,  of  a  crucible,  which  is  placed  in  circuit  by  means  of 
carbon  contacts,  so  that  the  current  passes  vertically 


36      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

through  the  crucible  walls.  Helberger  uses  the  ordinary  carbon 
or  graphite  crucibles. 

Before  using  these  crucibles  they  are  prepared  by  a  patented 
process  which  permits  the  current  passage  through  the  crucible 
walls  only.  These  furnaces  were  originally  built  only  for  the 
handling  of  precious  metals.  As  communicated  by  the  firm  of 
Hugo  Helberger,  the  current  conduction  from  the  crucible  wall  to 
the  metal  contents  was  made  more  difficult  by  removing  the 
graphite  from  the  inner  surface  of  the  crucible.  This  graphite 
removal  is  accomplished  by  blowing  air  into  the  red-hot  crucible. 
As  long  as  the  material  is  not  molten  there  is  no  passage  of  the 
current.  As  soon  as  the  contents  becomes  fluid,  it  gets  into 
intimate  contact  with  the  red-hot  lining,  which  acts  as  a  Nernst 
filament  would,  so  that  some  electrical  energy  also  goes  through 
the  lining  and  directly  through  the  bath.  This  action  has  no 
deleterious  influence  on  the  charge,  as  the  metal  for  which  these 
small  furnaces  are  applicable  is  tapped  as  soon  as  it  is  molten, 
for  a  refining  of  the  charge  is  not  necessary  or  desired. 

If  these  furnaces  are  to  be  used  in  steel  works  for  small 
trial  melts,  for  which  they  seem  excellent,  carbon  crucibles 
are  used  which  are  nearly  always  lined  with  a  metal  oxide  from 
.4  to  1.2  inches  (10  to  30  mm.)  thick.  These  carbon  crucibles, 
so  the  inventor  advises,  need  only  half  the  voltage  of  the  graphite 
crucibles,  a  result  of  this  being  that  the  deviation  from  the  normal 
working  current  is  not  so  great,  so  that  in  this  way  it  is  possible 
to  practically  lead  the  current  entirely  through  the  walls  of  the 
crucible. 

The  practical  design  of  this  furnace  is  therefore  to  be  regarded 
as  having  been  well  done.  The  crucible  is  built  together  with 
a  regulating  transformer,  as  shown  by  Fig.  i8a.  The  upper 
carbon  contact  covers  the  heating  chamber  at  the  rim  only,  so 
that  the  process  going  on  in  the  crucible  may  easily  be  observed. 
The  crucible  is  protected  against  radiation  by  a  fire-brick  cylinder. 
The  clamping  arrangements  holding  the  carbon  contacts  are 
water-cooled.  The  size  of  the  Helberger  furnace  is  limited  on 
account  of  the  difficulty  encountered  when  manufacturing  larger 
crucibles.  Yet,  the  manufacturers,  The  Helberger  Co.,  of 


EFFECTS   OF   THE   ELECTRIC   CURRENT  37 

Munich,   Germany,  state  that  furnaces,  up  to  a  capacity  of 
300  Kg.  (660  Ibs.),  are  being  successfully  built  to-day. 

4.  ARC    HEATING 

When  counting  the  various  possible  ways  of  heating  we  must 
not  forget  to  mention  the  electric  arc  for  this  has  found  the 
widest  application  in  the  iron  industry.  We  will  spend  much 
time  in  the  following  chapters,  therefore,  with  arc  heating  and 
arc  furnaces.  They  are  mentioned  here  only  for  the  sake  of 
completeness. 

CHEMICAL  ACTION 

Besides  the  purely  thermal  action  of  the  electric  current  the 
mill  man  will  also  be  interested  in  the  chemical  action  which 
takes  place  when  an  electric  current  is  passed  through  a  liquid. 
The  best  known  example  of  this  is  the  disassociation  of  water 
into  its  constituents,  oxygen  and  hydrogen.  This  may  be 
observed  by  passing  a  direct  or  continuous  current  through 
water.  In  so  doing  the  well-known  reaction  takes  place  as 
oxygen  is  given  off  at  the  positive  pole  and  hydrogen  at  the 
negative  pole. 

To  this  belongs  also  the  best  known  electro  metallurgical 
application  of  electrolytic  action  for  the  smelting  of  aluminum. 
According  to  the  method  first  proposed  by  Heroult  and  Hall, 
both  in  1887,  the  clay  is  melted  by  the  action  of  arc  heating,  and 
simultaneously  the  molten  mass  is  separated  electrolytically  in 
such  a  way  that  the  aluminum  is  freed  and  collected  at  the 
negative  pole,  whereas  at  the  hanging  positive  carbon  electrode 
the  oxygen  is  set  free,  and,  together  with  the  carbon  of  the 
electrode,  escapes  as  carbonic  acid  gas. 

These  examples  are  sufficient  to  show  how  chemical  action 
may  be  brought  about  by  the  electric  current.  In  this  instance 
it  is  to  be  observed  that  this  action  only  occurs  when  direct 
current  flows  through  the  electrolyte  to  be  separated.  If  on  the 
other  hand  alternating  current  is  used,  where  the  current  direction 
is  constantly  changing,  then  no  electrolytic  action  can  take  place. 
For  supposing  we  had  an  apparatus  for  the  dissociation  of  water, 
which  was  supplied  with  alternating  instead  of  continuous  current. 


38      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Then  during  one  moment  with  the  current  in  one  direction,  we 
would  obtain  oxygen  at  the  electrode,  and  during  the  next 
moment  with  the  reversed  current  direction  we  would  receive 
hydrogen.  It  is  evident,  therefore,  that  electrolytic  effects  do 
not  arise  when  alternating  current  is  used. 

From  this  it  also  follows  that  molten  iron  masses  of  electric 
furnaces,  through  which  current  passes,  are  not  subject  to  any 
chemical  action  as  long  as  alternating  current  is  used.  We 
could  in  any  event,  as  in  the  above  example,  assume  a  momentary 
chemical  action,  which  however  would  be  reversed  in  the  next 
moment,  for  even  though  it  appears  momentarily,  it  does  not 
come  into  play  as  far  as  the  metallurgical  process  is  concerned. 
This  assumes  that  the  reversal  of  the  chemical  effect  is  not 
interrupted. 

When  using  direct  current  in  iron  baths,  electrolytic  action 
naturally  occurs,  by  which  iron  sulphides  and  iron  phosphides 
may  be  separated.  These  suggestions  have  also  found  their 
way  into  the  patent  office. 

Electrolytic  actions  may  however  be  positively  harmful  for 
carrying  out  metallurgical  processes.  According  to  Conrad 
(see  Stahl  u.  Eisen,  1909,  p.  796)  we  obtain  a  purer  product  when 
using  alternating  current  for  the  manufacture  of  ferro  silicon, 
than  when  using  direct  current.  For  when  using  continuous 
current  the  impurities  of  the  charge  are  reduced,  such  as  calcium, 
aluminum  and  other  metals,  which  then  find  their  way  into  the 
final  product. 

The  designers  of  the  electric  furnaces  for  the  iron  industry 
today  use  alternating  current  exclusively,  because  they  fear  the 
undesirable  influences  in  the  charge  due  to  direct  current.  It 
may  not  be  out  of  place  to  quote  the  words  here  of  an  ardent 
supporter  of  electric  furnaces  for  the  iron  and  steel  trades.  We 
quote,  therefore,  from  Prof.  Borchers  and  his  address  in  1905,  a 
translation  of  which  might  be  called: 

"Electrolytic  effects  were  not  sought  in  most  reduction  and 
melting  tests,  whether  they  endeavored  to  produce  pig  iron,  or 
make  steel,  even  though  these  electrolytic  effects  are  nowhere 
entirely  eliminated.  This  was  particularly  so  in  the  arc  proc- 


EFFECTS  OF  THE  ELECTRIC  CURRENT  39 

esses  of  earlier  periods,  where  testers  positively  failed,  when 
endeavoring  to  produce  irons  low  in  carbon.  If  for  instance  the 
iron  to  be  smelted  makes  one  pole  of  the  arc,  and  carbon  blocks 
the  other,  then  the  iron  absorbs  carbon  equally  well,  whether 
direct  or  alternating  current  be  used.  We  know  that  an  arc 
between  two  carbon  poles  carries  carbon  vapor  across  from  one 
pole  to  the  other.  For  the  evaporating  point  of  carbon  deter- 
mines the  arc  temperature.  If  one  of  the  poles  consists  of  iron, 
then  the  only  material  remaining  for  the  other  pole  is  carbon, 
provided  direct  arc  heating  is  used.  In  this  way  the  iron  will 
gradually  become  saturated  with  carbon  even  with  alternat- 
ing current.  Though  we  assume  that  the  carbon  in  the  arc 
wanders  only  from  the  anode  (positive  pole)  to  the  cathode 
(negative  pole),  it  is  evident  that  the  carbon  separates  itself  in 
its  solution  in  such  a  way,  during  a  current  wave,  in  going  from 
the  carbon  pole  to  the  iron,  that  only  a  small  part  of  it  would 
return  during  the  current  alternation." 

We  perceive,  therefore,  that  we  must  guard  against  the 
harmful  absorption  of  carbon  by  suitable  mean's,  when  using 
furnaces  operating  with  carbon  electrodes,  even  when  working 
with  alternating  current. 

This  is  accomplished  today  by  interposing  a  layer  of  slag 
between  the  arc  and  the  iron,  in  all  furnaces  where  the  arc  im- 
pinges directly  on  the  metal.  This  slag  is  then,  to  be  sure,  acted 
upon  in  a  reducing  manner  by  the  arc,  yet  the  iron  is  protected 
from  any  union  with  carbon. 

In  accordance  with  the  foregoing,  then,  we  may  definitely 
establish  that  no  electrolytic  action  takes  place  in  the  great 
majority  of  furnaces,  which  operate  exclusively  with  alternating 

current. 

MOTOR  EFFECT 

In  the  construction  and  operation  of  electric  furnaces  we 
have  to  take  into  account  the  motor  effect  of  the  electric  current 
as  well  as  the  thermal  and  chemical  effect. 

It  is  just  as  easy  to  transform  motion  into  electricity  as  the 
reverse,  as  is  very  evident  from  the  wide  application  of  the 
electric  motor. 


vsNA*'//> 
N|§.: 


40   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

It  exceeds  the  limits  of  this  book  to  explain  the  motor  phe- 
nomenon in  detail,  still  in  order  to  understand  and  have  a  correct 
opinion  of  the  possible  and  impossible  motions  of  the  molten 
metal  in  electric  furnaces,  it  appears  desirable  at  least  to  discuss 
briefly  the  reasons  for  the  motion  phenomena. 

It  is  well  known  that  an  ordinary  magnet  attracts  a  piece  of 
iron  brought  into  its  vicinity,  and  that  motion  is  caused  by  means 
of  this  magnetism.  It  is  equally  well  recognized  that  two  magnets, 
like  magnetic  poles,  repel  one  another;  while  unlike  poles  attract 
one  another. 

We  also  speak  of  lines  of  force,  which  surround  the  space 
near  a  magnet,  and  it  is  to  these  lines  of  force  issuing  from  a 

magnet  that  we  attribute  the 
/  /     ^--  ~"~^^^^  \       distant  magnetic  effect.    Sup- 

1 1  /^"'"'_ _~_V^^\\\  !    *  pose  we  have  two  magnets  as 

Fig.  19  shows  with  their  like 
poles  laid  next  to  each  other. 
If  we  draw  the  path  of  the 
lines  of  force  as  shown  we 
may  define  the  repelling  action 
of  like  poles,  by  saying : 

Lines  of  force  having  the 

\\  ^--^ -^--"''X  /         same  direction  repel  each  other; 

those  of  opposite  direction 
attract  each  other. 

We  also  obtain  motion  phenomena,  therefore,  in  accordance 
with  this  rule,  as  a  result  of  two  magnets  acting  on  each  other. 
But  we  will  also  have  these  motion  phenomena,  if  a  stationary 
current  carrying  conductor  is  brought  near  an  ordinary  suspended 
magnet.  In  order  to  do  this  we  may  set  up  an  easily  movable 
magnetic  needle  in  its  case,  and  directly  above  it  stretch  a  wire, 
which  may  be  connected  to  a  source  of  electricity.  As  soon  as 
the  current  is  switched  on,  the  needle  will  endeavor  to  set  itself 
at  right  angles  to  the  wire.  The  size  of  the  deflection  is  a  direct 
measure  of  the  current  passing  through  the  wire.  We  find  that 
the  deflecting  power  decreases  as  the  conductor  is  moved  away 
from  the  magnet  parallel  to  itself;  that  the  direction  of  the 


EFFECTS   OF  THE  ELECTRIC  CURRENT 


41 


needle  is  reversed  when  the  wire  is  under  instead  of  above  the 
needle;  and  that  at  every  position  the  deflecting  power  is  pro- 
portional to  the  current. 

These  phenomena  prove  that  a  current  carrying  wire  is 
surrounded  by  lines  of  force  throughout  its  whole  length,  whose 
density  is  greater  in  the  immediate  vicinity  of  the  wire,  which 
decreases  as  the  distance  from  it  (the  wire)  increases.  Accord- 
ingly we  may  imagine  the  fields  of  force  of  a  current  carrying 
wire  about  as  shown  by  Fig.  20.  It  is  assumed  here  that  the 
conductor  pierces  a  sheet  of  paper.  On  this  are  drawn  the  lines 
of  force  as  they  would  appear  when  the  current  flows.  The  proof 
of  these  lines  of  force  existing 
concentric  to  the  conductor  may 
easily  be  had,  if  a  glass  plate  is 
used  in  place  of  the  paper,  which 
is  strewn  with  iron  filings.  If  an 
electric  current  is  then  sent 
through  the  wire,  which  pierces 
the  plate,  the  iron  filings  will 
arrange  themselves  in  direction 
and  density,  in  accordance  with 
the  lines  of  force.  The  direction 
of  the  lines  of  force  may  then  be 
established  in  compliance  with 
a  single  rule:  //  the  current 
carrying  conductor  is  grasped  in 
the  right  hand  so  that  the  out- 

stretched thumb  indicates  the  direction  of  the  current,  then  the  lines 
of  force  will  encircle  the  wire  so  that  they  would  issue  from  the  ends 
of  the  remaining  fingers. 

If  we  now  return  to  the  first  test,  in  which  a  movable  magnet 
was  brought  into  the  magnetic  field  of  an  electric  conductor, 
then  in  diverting  the  magnet  we  have  a  motion  phenomena, 
pursuant  to  mechanical  power,  which  appears  between  electric 
currents  and  magnets. 

We  can  now  go  a  step  further  and  replace  the  second  magnet 
by  a  conductor,  through  which  current  flows.  Even  then  certain 


i~o  ftWb  tfV9^" 


FIG.  20. 


42      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

phenomena  will  be  observable,  provided  one  of  the  conductors 
carrying  current  is  movable.  For  until  now,  we  have  found  that 
the  motion  phenomena  are  the  result  of  magnetic  fields  which 
mutually  affect  each  other.  As  we  have  also  seen  that  each 
conductor  carrying  current  has  its  own  magnetic  field,  then,  in 
accordance  with  the  foregoing,  the  appearance  of  mechanical 

power  is  unavoidable, 
between  current  carrying 
conductors  lying  closely 
together. 

Accordingly    we     may 
immediately  determine  the 
direction    of    the    motion. 
FlG-  2I-  Suppose  we  have  two  con- 

ductors    both     of     which 

carry  current  going  in  the  same  direction,  as  shown  by  Fig.  21 
at  a  and  b,  here  the  current  would  be  flowing  toward  the  reader. 
According  to  the  foregoing  rule  the  direction  of  the  lines  of  force 
is  quickly  determined  and  is  shown  by  the  arrows.  We  see, 


FIG.  22. 

therefore,  in  the  space  between  the  .two  conductors  that  the 
direction  of  the  lines  of  force  are  opposite  to  each  other.  As 
the  lines  of  force  of  opposite  direction  attract  each  other,  we  may 
say  relative  to  the  current:  "Currents  of  like  direction  attract  each 
other  "  and  "currents  of  opposite  direction  repel  each  other." 


EFFECTS  OF  THE  ELECTRIC  CURRENT 


43 


From  this  it  follows  that  crossed  currents  and  their  con- 
ductors (as  shown  by  Fig.  22)  endeavor  to  arrange  themselves 
parallel  to  each  other,  and  in  such  a  way  that  the  current 
in  both  flows  in  the  same  direction.  That  is,  the  movable 
conductor  a  tries  to  assume  the  same  direction  as  the  stationary 
conductor  b. 

The  case  is  also  very  interesting  where  one  current  flows 
vertically  to  the  other,  as  shown  by  Fig.  23.  Here  the  circles  or 
dots  represent  the  points  of  the  arrows,  which  indicate  the 
direction  of  the  lines  of  force,  while  the  crosses  represent  the 
ends  of  these  arrows. 

As  lines  of  force  in  the  same  direction  repel  each  other,  and 
those  of  opposite  direction  attract,  then  the  movable  conductor 
a  will  endeavor  to  move  in  the  direction  as  shown  by  the  arrow. 


+ 

0 

+ 

o 

+ 

o 

o     o     o     o      o     o  > 

'   0        0 

0000 

+       ••-       +       +       +      +          +       +       -f++       + 

FIG.  23. 

In  place  of  the  above  simple  case  we  may  throw  some  light 
on  the  possible  motion  phenomena  in  arc  furnaces,  which  may 
arise  due  to  the  electrical  conditions  which  have  their  electrodes 
pointed  directly  against  the  bath. 

We  may  have  the  effect  of  two  or  more  currents  acting 
on  each  other.  In  this  case  one  of  the  conductors,  namely  the 
molten  metal,  may  be  regarded  as  being  movable,  within  certain 
limits.  For  the  molten  conductor  may  be  mechanically,  com- 
paratively easily  influenced,  even  if  only  within  the  limits  of  the 
hearth. 

The  conditions  are  also  very  similar  with  induction  furnaces, 
excepting  that  in  the  place  of  the  one  solid  conductor,  we  have  a 


44      ELECTRIC  PURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

coil  of  many  turns.  Figs.  24  and  25  show  how  the  lines  of  force 
act:  in  the  former  case  with  the  turns  wound  far  apart,  and 
latterly  with  the  turns  wound  closely  together.  It  follows, 
therefore,  that  coils  such  as  these  are  surrounded  by  like  lines 
of  force  as  common  rod  magnets  would  be,  and  thereby  the  laws 
are  known  which  govern  the  motion  phenomena  between  active 
coils  and  single  conductors. 

Aside  from  the  above  explanations  it  still  seems  desirable 
to  mention  a  very  special  motion  in  molten  conductors,  through 

which  current  is  passing,  but 
which  only  arises  in  certain 
cases.  This  is  the  so-called 
"pinch  effect." 

According  to  an  address  by 
Carl  Hering  before  the   Cana- 
dian meeting  of  the  "American 
Electrochemical     Society,"      in 
^     ^     ^  May,    1909,    this    pinch    effect 
FlG-  24-  occurs      when      a      continuous 

or    alternating     current     flows 

through  a  molten  conductor.  Then  this  conductor  endeavors 
to  contract  itself  in  the  line  of  its  cross-section  under  the 
action  of  electro-magnetic  forces.  The  contracting  force  is 
only  small,  when  the  current  density  is  low,  but  grows  with  in- 
creasing current  density  (amperes  per  square  millimetre  or  square 
inch),  and  can,  in  extreme  cases,  become  so  large,  that  the  cross- 
section  at  the  contracting  point  may  decrease  to  zero,  thereby 
interrupting  the  current.  The  contraction  primarily  occurs  at 
such  places  in  the  hearth  which  have 
already  been  contracted  owing  to  occa- 
sional irregularities  when  tamping  the 
lining  material  in  place.  The  fluid  FIG.  25. 

column  of   metal    conducting    current  is 

therefore  interrupted  at  the  weakest  place  in  its  cross-section, 
exactly  as  a  rope  breaks  at  its  weakest  place.  In  addition  to  this, 
there  is  a  depression  where  the  cross-section  diminishes,  and  on 
this  slanting  fluid  conductor,  particles  of  slag  and  the  like  are  apt 


EFFECTS  OF  THE  ELECTRIC  CURRENT          45 

to  follow,  which  then  cause  a  further  increase  in  the  current 
density,  as  the  conductivity  of  these  impurities  is  less  than  that  of 
the  molten  metal.  Furthermore  this  would  be  caused  at  places 
where  the  cross-section  is  already  weakened,  so  that  thereby  the 
actions  of  the  pinch  effect  would  be  still  further  increased. 

This  course  of  things,  as  pictured  above,  does  not  take  place 
in  any  deleterious  or  unpleasant  fashion  with  electric  furnaces 
as  they  are  used  for  the  most  part  in  the  iron  industry  today. 
As  the  pinch  effect  only  appears  with  comparatively  high  current 
densities,  we  find  that  it  does  not  occur  at  all  in  arc  furnaces. 
But  it  causes  various  motion  phenomena  with  induction  furnaces, 
as  we  shall  presently  explain.  Motion  phenomena  which  are 
entirely  desirable  and  advantageous  for  the  working  of  metal- 
lurgical processes,  may  be  brought  about  by  artificially  narrowing 
the  cross-section  of  the  bath  to  accomplish  the  required  result. 
These,  by  their  very  nature, 
would  in  no  way  endanger  the 
electrical  furnace  operation. 

An  explanation  of  the  appear- 
ance of  the  pinch  effect  may  be 
had,  if  we  assume  that  the  FJG  26 

fluid  mass  is  composed  of  many 

parallel  connected  conductors,  which  are  all  leading  like  direc- 
tional currents  through  them.  As  currents  having  the  same 
direction  attract  each  other,  the  foregoing  sentence  is  applicable 
here,  for  in  a  measure  it  defines  the  contracting  effect. 

In  electrical  furnaces,  where  the  pinch  effect  causes  motion, 
the  liquid  seems  to  be  driven  along  a  straight  line  from  the 
middle  and  the  centre  axis  toward  the  ends,  so  that  the  fluid 
mass  is  lower  in  the  centre  than  at  either  end.  The  weight  of  the 
molten  metal  then  causes  a  flow  from  the  higher  lying  parts, 
toward  the  lower  middle  section,  as  shown  by  Fig.  26.  Here 
the  molten  conductor  is  considered  to  be  cut  vertically,  in  the 
line  of  the  horizontally  running  current.  Without  going  into 
further  details,  it  is  evident  that  the  motion  due  to  the  pinch 
effect  causes  an  intensive  mixing  of  the  charge.  This  occurs  as 
long  as  the  correct  agitation  is  maintained  within  the  desired 


46     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

limits,  for  the  motion  can  only  advantageously  effect  a  rapid 
chemical  reaction,  which  is  needed  between  the  iron  bath  and  the 
slag.  Besides  this  the  quality  of  the  steel  can  only  be  bettered 
by  the  greatest  possible  uniformity  which  is  brought  about  by 
this  circulation. 


CHAPTER  IV 

POWER  FACTOR  (COS  0)  AND  ALTERNATING  CURRENT 
THEORY  IN   GENERAL 

IN  the  previous  chapter  it  was  shown  that  direct  current, 
due  to  its  chemical  action,  is  totally  unadapted  for  electric  fur- 
naces as  used  in  the  steel  industry,  and  alternating  current  is 
therefore  used  exclusively  to  operate  electro-steel  furnaces. 

The  difference  between  direct  current  and  alternating  current 
is  that  in  the  former  the  current  is  always  flowing  in  the  same 
I 


FIG.  27. 


FIG.  2-ja. 


direction,  whereas  in  the  latter  it  changes  its  direction  con- 
tinually. 

The  required  time  for  one  directional  change  is  called  the 
period  and  is  designated  by  T.  Fig.  270  shows  a  complete  wave 
or  cycle.  In  this  figure  one  cycle,  therefore,  takes  the  time,  T, 
which  is  necessary  for  the  current  to  swing  through  a  complete 
wave.  Hence,  one  complete  cycle  goes  from  O  through  to  the 
positive  maximum,  and  from  zero  to  the  negative  maximum 
and  back  to  the  zero  point. 

For  all  practical  purposes  we  can  assume  that  the  usual 
alternating  current  generator  gives  a  sine  wave  for  its  electro- 
motive force.  This  being  the  case,  it  only  remains  to  show  how 

47 


48      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

a  sine  curve  is  constructed,  and  to  draw  another  diagram  next 
to  Fig.  270  showing  these  relations  in  alternating  current 
circuits. 

If  (as  in  Fig.  27)  we  let  the  radius  or  radius  vector  equal  the 
maximum  voltage  reached  in  this  sine  curve,  and  designate  this 
maximum  value  by  e,  the  various  instantaneous  values  of  the 
sine  curve  by  e'  ',  then: 

e'  =  e  sin  a 

i.e.,  for  every  angle  a,  the  ordinates  of  the  sine  curve  give  the 
corresponding  instantaneous  potential  values  as  indicated  by 
Fig.  27.  In  the  above  equation  in  place  of  the  angle,  however, 
we  can  substitute  for  it  the  value  of  the  angular  velocity  and 
obtain  : 

a  =  m  t 

(similar  to  the  equation,  distance  =  speed  X  time),  and  as  the 
angular  velocity  w  =  -77  hence 

e'  =  e  sin  m  t 

where  /  is  the  time  taken  by  the  radius  vector  until  it  has  passed 
through  the  angle  a  after  leaving  the  zero  or  starting  point.  The 
whole  time  corresponding  to  one  cycle  is  T  and  the  corresponding 
angle  is  2  IT,  and  by  substituting  these  values  in  the  previous 
formula,  since  (a  =  2  IT  and  t  =  T) 

2  TT  =  m  T  from  which  it  follows  that— 


It  is  customary  to  speak  of  cycles  per  second  or  frequency, 
and  as  the  time  of  one  cycle  is  equal  to  T,  the  frequency  u  is 


If  we  substitute  this  value  in  the  formula  containing  m,  we 
get  m  =  2  TT  v. 

We  speak  of  an  alternating  current  of,  say  25  cycles,  when 
this  current  makes  25  waves  each  second. 

The  more  or  less  frequently  varying  direction  and  strength 
of  the  current  depending  upon  the  cycles  per  second,  or  frequency, 


POWER  FACTOR  (COS  0)  AND  ALTERNATING  CURRENT  THEORY    49 

has  a  particular  bearing  on  the  functions  of  alternating  current 
circuits.  In  order  to  understand  these,  the  so-called  induction 
will  next  be  briefly  described.  This  seems  necessary  because  a 
clear  conception  of  the  induction  phenomena  is  important,  in 
order  to  understand  the  induction  furnaces  which  will  later  be 
discussed  in  detail. 

We  obtain  an  inductive  action,  for  instance,  when  an  electric 
conductor  is  moved  through  a  magnetic  field  so  that  magnetic 
lines  of  force  are  cut.  If  we  connect  the  ends  of  this  conductor 
with  a  measuring  instrument  we  obtain  a  deflection,  showing 
the  presence  of  an  electric  current  produced  by  induction.  This 
current  is  called  induced. 

We  therefore  say,  "  If  a  conductor  is  moved  in  a  magnetic  field 
so  as  to  cut  magnetic  lines  of  force,  an  electro-motive  force  is  produced, 
which  will  cause  a  current  to  flow  provided  that  the  conductor  has 
its  ends  closed  so  as  to  form  an  electric  circuit.  The  electro-motive 
force  and  also  the  current  become  larger,  as  more  magnetic  lines  of 
force  are  cut  in  a  given  time." 

It  is  evident  that  it  makes  no  difference  in  which  way  the 
magnetic  field  is  produced,  because  it  is  only  necessary  for  the 
conductor  to  cut  lines  of  force.  It  is,  therefore,  immaterial 
whether  the  conductor  is  moved  through  the  field  of  a  permanent 
magnet  or  through  the  field  of  an  electro-magnet.  It  is  even 
sufficient  to  move  it  near  a  wire  through  which  a  current  is 
flowing,  because  this  wire  is  surrounded  by  lines  of  force. 

Until  now  we  have  assumed  that  we  have  moved  the  con- 
ductor in  which  a  current  is  induced.  Instead  of  that  we  can 
move  the  magnet  and  hold  the  conductor;  still,  as  in  that  case, 
an  electro-motive  force  is  also  generated,  due  to  lines  of  force 
being  cut.  We  may  finally  place  two  conductors  side  by  side, 
and  if  we  pass  a  current  through  one  of  them,  it  will  generate  a 
magnetic  field,  the  lines  of  force  of  which  will  cut  the  second 
conductor.  If  the  current  is  interrupted,  the  lines  of  force  dis- 
appear, only  to  reappear  instantly  upon  the  current  being  again 
made.  We  therefore  have  a  field  of  constantly  changing  lines 
of  force  and  a  conductor  located  in  this  field.  Hence  an  e.m.f. 
is  induced  in  the  second  conductor,  exactly  as  when  a  magnet 


50      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

approaches  a  conductor  from  an  infinite  distance  and  then  recedes 
again  to  an  infinite  distance. 

The  alternating  current  changes  its  strength  continually,  and, 
as  we  have  seen,  it  increases  twice  during  each  period  or  cycle 
from  zero  to  a  maximum  and  consequently  decreases  from  that 
point  again  to  zero.  As  a  result  of  this,  a  conductor  carrying 
an  alternating  current  is  surrounded  by  an  alternating  magnetic 
field,  which  induces  e.m.f.,  or  currents,  in  all  conductors  within 
its  field. 

The  current-carrying  conductor  itself  thus  lies  in  an  alternat- 
ing field  and,  from  what  has  been  said,  it  is  evident  that  an  e.m.f. 
will  be  induced  in  this  conductor  by  its  own  field.  This  action 
is  called  self-induction,  and  the  current  generated  thereby  is 
called  the  self-induced  current. 

This  self -induced  current  always  flows  in  the  opposite  direction 
to  the  current  which  produces  it.  If  the  primary  current,  for 
instance,  flows  to  the  right,  the  induced  current  will  flow  in  the 
opposite  direction,  or  to  the  left,  in  the  same  conductor.  The 
self-induced  current  for  this  reason  does  not  exist,  as  the  effect 
is  to  weaken  the  primary  current.  If  voltage  is  applied  to  a  coil, 
therefore,  the  current  does  not  immediately  reach  its  maximum 
value,  but  does  so  only  after  a  certain  time-interval  has  elapsed. 
The  highest  value  is  reached  after  the  lines  of  force  are  no  longer 
on  the  increase.  We  therefore  say  the  current  lags  behind  the 
voltage. 

It  should  be  remembered  that  we  obtain  the  instantaneous 
values  of  the  voltage  as  the  projections  of  a  rotating  radius 
vector.  Therefore,  we  can  likewise  get  the  instantaneous  values 
of  the  current  as  projections  of  a  radius  vector  of  a  different 
value.  We  then  obtain  the  lag  of  the  current  behind  the  voltage, 
and  draw  this  lag  out  in  the  form  of  a  definite  angle.  This  angle 
is  then  the  measure  of  the  lag.  Time  difference  between  current 
and  voltage  we  call  phase  displacement, — and  the  angle  which 
the  radii  vector  of  the  current  and  voltage  make  with  each  other 
is  called  the  phase  angle.  The  letter  0  has  been  commonly  chosen 
to  designate  this  angle. 

We  have  for  instance  the  vector  diagram  Fig.   28.,  which 


POWER  FACTOR  (COS  0)  AND  ALTERNATING  CURRENT  THEORY  51 

pictures  the  relations  as  they  might  be  in  an  alternating  current 
circuit.  We  have  only  to  imagine  the  radii  vector  as  rotating 
about  0  as  a  centre,  to  obtain  at  any  time  the  corresponding 
values  of  the  current  and  voltage  by  drawing  the  vertical  pro- 
jections of  their  respective  radii  vectors. 

Sometimes  this  vector  diagram  is  drawn  even  more  simply, — 
see  Fig.  29. 

On  what  conditions  now  does  this  phase  displacement  depend? 

We  have  already  seen  that  this  phase  displacement  is  a 
result  of  the  self-induction.  Therefore,  the  greater  the  current 


FIG.  28.  FIG.  29. 

and  the  faster  the  changes,  the  greater  is  the  change  in  the 
corresponding  magnetic  fields,  in  a  given  time.  The  frequency 
therefore,  has  a  large  influence  on  the  phase  displacement. 

Besides  this,  the  self-induction  is  also  dependent  on  the  type 
of  conductor  used  and  its  position  relative  to  other  conductors. 
The  factor  which  designates  these  conditions  is  called  the  "co- 
efficient of  self-induction."  The  mathematical  symbol  for  this 
is  "L." 


52   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

We  therefore  say: 

The  electro-motive  force  of  self-induction  is  proportional  to  the 
coefficient  of  self-induction,  and  to  the  rate  of  change  of  current  per 
second,  or  the  frequency. 

If  we  compare  the  relations  in  an  alternating  current  circuit 
with  those  in  a  direct  current  circuit,  we  see,  in  the  latter  case, 
that  it  takes  a  definite  voltage  to  force  a  current  i,  through  the 
resistance  r,  and,  according  to  Ohm's  Law,  we  have 
e  =  iX  r 

If  it  is  desired  to  send  an  equal  alternating  current,  *,  through 
a  coil,  it  also  takes  a  certain  voltage, 

er  =  *  X  r, 
to  overcome  the  resistance. 

We  have  to  take  into  account,  though,  that  with  alternating 
current  an  electro-motive  force  due  to  self-induction  is  generated, 
which  is  always  in  the  opposite  direction  to  the  impressed  electro- 
motive force. 

In  order,  therefore,  to  obtain  the  desired  current  i,  we  need 
not  only  the  voltage,  er  =  i  r,  but  also  an  additional  pressure 
eL  to  overcome  the  electro-motive  force  of  self-induction.     Hence, 
the  total  voltage  necessary  for  an  alternating  current  is, 
e  =  er  +  eL. 

The  alternating  current  voltage  e  is  composed  of  two  different 
pressure  waves.  These  waves  are  displaced  by  an  angle  of  90° 
or  %  of  a  period,  which  can  easily  be  shown  by  a  short  mathemati- 
cal demonstration. 

The  above  sentence  in  italics  regarding  self-induction,  is 
mathematically  expressed  as  follows: 


Furthermore,  we  know  that  for  a  sine  wave,  the  formula  for 
an  alternating  current  at  any  instant  is: 

i'  =  I  sin  m  t, 
exactly  as  the  sine  wave  for  the  voltage  gave 

e'  =  e  sin  m  t. 


POWER  FACTOR  (COS  #)  AND  ALTERNATING  CURRENT  THEORY   53 


If  we  substitute  another  value  for  i  in  the  equation 

r   di 
eL  =  L  —;—  we  obtain 

di       d(l  sin  m  i) 

_^  _  _  _  _  m  i  cos  m  i 

dt  dt 

e'L  =  (mXiX  L)  cos  m  t. 
We  have  er  =  i  r  or  the  instantaneous  value 

e'r  =  (i  r)  sin  m  t. 
The  total  voltage  is,  therefore, 

e'  =  e'r  -f  e'L  =  (i  r)  sin  m  t  -f-  (i  m  L)  cos  m  t 
and  as  cosmt  =  sin  (m  t  +  90°)  B 

it  is  evident  that  the  voltage  e?=ir) 
necessary  to  overcome  the  coun- 
ter electro-motive  force  of  self- 
induction  is  90°  ahead  of  the 
e.m.f.  necessary  to  overcome  the 
ohmic  resistance.' 

From  this  it  follows  that 
these  two  e.m.f.'s  are  not  to  be 
added  arithmetically  but  geo- 
metrically. If  we  draw  this  as 
shown  in  Fig.  30,  we  have : 

O  A  =  maximum  value 
of  the  current  =  i 


FIG.  30. 


The  resultant  of  the  two  e.m.f.'s  is  graphically  shown  as  O  D, 
and  from  it  we  obtain  the  total  voltage 

e  =  er  +  eL. 
From  the  figure  then  we  have: 


=  i  V  r  +  m2  U 
It  also  follows  that  tan  0  =  -y-  when  <f>  is  the  phase  angle 


54      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

between  the  current  and  the  voltage. 

It  is  worthy  of  mention  that  from  the  equation 

e  =  i  vV  -f  mr  L 

it  seems  as  though  the  self-induction  apparently  increases  the 
resistance.     Hence,  the  expression 


is  also  called  the  "apparent  resistance"  of  an  alternating  current 
circuit.  In  order  that  there  shall  be  no  mistake  regarding  the 
values  which  are  indicated  by  measuring  instruments  in  alternat- 
ing currents,  it  is  well  to  emphasize  here,  that  so  far  we  have  only 
mentioned  the  instantaneous  and  maximum  values.  As  a  matter 
of  fact,  neither  of  these  values  is  indicated  by  the  usual  alternat- 
ing current  instruments.  These  values  have  only  been  used  to 
more  clearly  state  the  relation  in  a.c.  and  to  make  them  easier 
to  understand.  The  instantaneous  and  maximum  values  are 
therefore  only  of  theoretical  interest,  whereas  the  a.c.  instruments 
indicate  a  so-called  "effective  value."  This  is  obtained  from  the 
previous  formulas  and  figures  by  dividing  the  maximum  values 

—  e 

by  \/2.     Hence,  the  effective  value  of  the  voltage  is  e  =  —=  and 

the  effective  value  of  the  current  is 

'i 

l  =  vl. 

We  can  therefore  regard  the  diagrammatic  figures  as  representing 
the  effective  values,  as  these  only  differ  from  the  maximum  values 
by  a  constant  factor. 

If  we  now  return  to  the  phase  displacement  between  the 
current  and  voltage,  we  find  the  question  becomes  of  the  greatest 
interest. 

What  influence  has  the  phase  displacement  on  the  power 
computation  ? 

It  was  shown  in  Chapter  II.  that  the  power  in  watts  is  equal 
to  the  product  of  the  current  and  voltage,  that  is  p  =  e  X  i. 
Unless  the  so-called  power  factor,  which  will  be  later  explained,  is 
unity,  this  last  equation  is  only  applicable  to  direct  current. 


POWER  FACTOR  (COS  </>)  AND  ALTERNATING  CURRENT  THEORY   55 

Whereas  for  alternating  current  the  formula  becomes, 

p  =  e  i  cos  0. 

In  this  equation  e  is  the  effective  voltage,  i  the  effective  current 
and  cos  </>  the  power  factor. 

In  alternating  current  circuits  we  call  the  product  e  X  i  the 
apparent  power.  It  is  measured  in  volt-amperes  or  kilo-volt- 
amperes  =  1000  volt-amperes.  The  product  e  i  cos  <f>  designates 
the  real  or  effective  power  and  is  measured  in  watts  or  kilowatts. 
To  verify  the  equation  for  the  true  power  really  goes  beyond  the 
limits  of  this  book.  For  those,  therefore,  who  are  interested  in 
this  paragraph,  it  is  added  in  an  abbreviated  manner. 

The  equation  for  the  instantaneous  energy  is 
p'  =  e'  X  »'. 

T 

The  work  done  in  %  a  period  during  the  time  —  is  then 

r- 

A  =Jo2  e'i'dt 
and  from  this  we  obtain  the  mean  value  of  the  energy. 

JL      L  L 

p  =  £  /••  e'i'dt  =  -j  C2  e'i'dt 

2  J o  "a 

by  substituting  the  values  i'  =  I  sin  m  t  and 

e'  =  e  sin  (mt  +  <j>) 
and  by  completing  the  integration,  we  obtain, 

el 
p  = cos  0  and  as 

e  I 

—7=  =  e  and  —=  =  *  we  get  £  =  e  *  cos <£. 

V2  V2 

From  this  it  follows  that,  providing  the  voltage  and  power 
remain  unchanged,  the  current  decreases  with  an  increasing 
power  factor.  As  the  current  strength  determines  the  cross- 
section  of  the  electrical  conductor,  it  naturally  interests  us  to  keep 
the  current  down,  i.e.,  we. strive  to  obtain  the  highest  possible 
power  factor. 

From  the   above  power    equation,  it   follows    that,   when 

COS0  =  I, 


56      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

p  =  e  i  and  the  angle  <£  =  o°.  The  other  limit  is  when 
cos  <f>  =  o  or  the  angle  4>  =  90°,  then  the  power,  p  =  o.  A  low 
power  factor,  therefore,  corresponds  with  a  large  phase  dis- 
placement. The  meaning  of  the  above  may  best  be  enlarged 
upon  by  an  example: 

Suppose  the  electrical  circuit  contains  a  coefficient  of  self- 
induction    L  =  .002  henry 
a  resistance  r  =  .0125  ohm 

a  frequency  v  =  50  and  therefore  m  =  2  TT  v  =  314 
voltage  e  =  150  volts. 

Then: 

mL       314  X  .002 

tan  <f>  = = —  =  50.24. 

r  -0125 

The  angle  <£  corresponding  to  this  value  is  then  88°  50'  or  nearly 
90°.     Hence  cos  <f>  is  nearly  zero. 

The  relations  are  graphically  shown  in  Fig.  31      This  shows 


FIG.  31. 

that  e  and  eL  almost  coincide,  so  that  eL  practically  equal  e. 
The  current  is  then 

e  iso 

i  = 7-  =    ,  0    =  240  amperes. 

mL       .628 

Consequently   ir  =  240  X  .0125  =  3  volts  =  ecos$ 
and 

i  X  e  cos  0  =  3  X  240  =  720  watts; 

With  the  same  current  but  with  cos  <£  =  i ,  we  would  have  ob- 
tained instead  of  the  above,  the  power  p  =  240  X  150  X  i  = 
36000  watts. 

This  example  shows  us  plainly  how  impossible  it  is  to  judge 
the  power  in  an  alternating  current  circuit  by  merely  reading 


POWER  FACTOR  (COS  #)  AND  ALTERNATING  CURRENT  THEORY  57 

the  ammeter  and  the  voltmeter,  as  these  two  instruments  do  not 
in  any  way  indicate  what  the  power  factor  is.  We  therefore  em- 
ploy a  special  instrument  to  measure  the  power,  a  so-called 
wattmeter,  which  indicates  the  watts  or  kilowatts,  directly, 
where 

i  kilowatt  =  i  kw  =  1000  watts. 

As  the  example  showed  that  the  voltage  necessary  to  overcome 
the  e.m.f.  of  self-induction  (i.e.,  the  vector  eL)  is  without  any 
influence  on  the  actual  power — in  other  words,  it  delivers  no 
power  which  can  be  measured  in  watts — we  therefore  call  this 
vector  the  wattless  component,  and  the  vector  er  =  i  X  r  is 
called  the  watt  component  of  the  voltage. 

Up  to  the  present  we  have  divided  the  voltage  into  two 
component  parts.  The  one  being  the  watt  component  er  —  ir 
which  coincides  with  the  direction  of  the  current,  the  second  being 
the  wattless  component  eL  =  i  m  L  which  is  in  quadrature  with 
the  former. 

The  power  p  =  e  i  cos  $  =  i  (  e  cos  </>)  where  e  cos  $  =  er', 
that  is,  the  power  is  obtained  by  multiplying  the  two  unidirec- 
tional vectors  or  forces  (i  and  er).  (See  Fig.  30.) 

Instead  of  separating  the  voltage  into  two  components,  we 
could  have  also  separated  the  current  into  two  forces  at  right 
angles  to  each  other.  This  separation  can  be  done  in  such  a  way 
that  one  force  falls  in  the  direction  of  the  terminal  voltage,  and 
being  multiplied  with  this,  it  gives  the  resultant  power,  while  the 
other  force  is  perpendicular  to  the  first  one. 

The  equation  for  the  power, 

p  =  eicos<f>  can  be  written 
as  p  =  e  (i  cos  </>)  =  e  ir 

where  ir  is  the  watt  component  of  the  current  and  equals  i  cos  <f>. 

Taking  then  the  values  of  the  example  as  chosen,  we  obtain 
Fig.  32.  The  directional  precedence  is  given  by  the  curved 
arrow.  Here  the  total  current,  i,  is  shown  as  lagging  behind  the 
voltage  by  the  angle  </>,  similarly  to  the  previous  example.  As 
the  angle  $  is  approximately  90°,  then  i  and  im  almost  coincide 
and  the  wattless  component  of  the  current  is 
i  =  im  =  240  amperes 


58      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

whereas  the  watt  component  of  the  current  ir  approximates  zero. 

It  is  therefore  apparent  that  the  total  current  im  is  only 
present  in  order  to  generate  the  e.m.f .  of  self-induction.  In  other 
words: 

It  is  the  wattless  component  of  the  current  which  generates 
the  lines  of  force.  That  is  why  this  wattless  current  is  also  called 
the  magnetizing  current,  and  this  is  why  it  is  designated  by  im 
in  the  accompanying  figure. 

It  follows,  therefore,  from  all  which  has  been  said  of  the  power 
factor  that:  When  figuring  the  size  of  electrical  conductors, 
the  apparent  power  should  always  be  the  determining  factor,  i.e., 
the  product  e  X  i  or  current  X  voltage,  in  other  words,  the 
kilo-volt  amperes.  On  the  other  hand,  the  power  of  the  prime 


FIG.  32. 

mover  only  takes  into  account  the  actual  power,  that  is  the 
product  e  i  cos  4>  or  the  actual  kilowatts.  In  other  words,  a  poor 
or  low  power  factor  means  expensive  lines  and  electrical  machinery, 
whereas  it  has  no  influence  whatever  on  the  prime  mover. 

It  is  apparent,  therefore,  that  it  is  in  the  interests  of  an 
inexpensive  installation  to  have  an  acceptable  power  factor.  It 
is  to  be  noted,  however,  that  in  the  ordinary  power  houses,  the 
power  factor  varies  between  .6  and  .8,  depending  on  the  sizes  of 
the  motors  used  and  at  what  load  these  are  operating.  These 
values  are,  therefore,  a  guide  indicating  whether  or  not  we  have 
a  good  power  factor. 

Quite  independent  of  the  current  lag,  we  may  have  induction 
phenomena  which  will  call  forth  other  and  more  disagreeable 
actions  than  those  shown,  and  as  it  is  the  object  in  designing  and 


POWER  FACTOR  (COS  <t>)  AND  ALTERNATING  CURRENT  THEORY  59 

operating  electric  furnaces  to  avoid  these  troubles,  we  will 
mention  them  briefly. 

We  have  seen  that  an  alternating  current  in  a  conductor  will 
generate  another  alternating  current  in  any  conductor  if  the  sec- 
ond conductor  only  lies  in  the  magnetic  field  of  the  first  conductor. 

We  therefore  obtain  currents  in  all  conductors  which  lie 
in  the  magnetic  field  of  another  conductor,  and  these  currents 
may  cause  considerable  power  losses  under  certain  conditions.  It 
would  lead  us  too  far  if  we  were  to  occupy  ourselves  deeply  with 
these  phenomena.  On  that  account  only  those  possibilities  will 
be  mentioned  which  lead  to  these  power  losses  in  electric  furnaces, 
and  the  remedies  which  help  to  overcome  these  losses. 

In  the  first  place  there  are  the  induced  currents  themselves, 
which  may  engender  considerable  losses.  As  these  induced 
currents  are  generated  in  every  conductor  which  is  parallel  to 
the  main  current,  they  may  cause  great  losses  when  the  conductor 
carrying  the  induced  current  is  short-circuited.  It  is  therefore 
necessary  to  avoid  all  designs  in  which,  for  example,  an  iron  beam 
would  follow  a  main  conductor,  so  that  it  would  then  be  short- 
circuited  on  itself.  This  condition  is  to  be  considered  only  when 
very  heavy  currents  are  present  as  is  altogether  the  case  with 
electric  furnaces.  But  even  here  these  actions  may  be  avoided 
by  carrying  the  incoming  and  outgoing  conductors  close  together. 
In  this  way  the  magnetic  fields— for  instance  those  made  by  the 
two  conductors  of  a  single  phase  circuit — are  then  neutralizing 
each  other,  so  that  we  have  no  action  on  parallel  lying  and  closed 
iron  parts.  There  are,  however,  currents  induced  in  every 
metal  part  which  is  near  an  alternating  current  carrying  con- 
ductor. These  metallic  parts  provide  splendid  conductors  for 
the  current  through  which  the  current  may  be  short-circuited, 
so  that  under  certain  circumstances  a  metallic  piece  of  that 
kind  may  reach  really  unlooked-for  temperatures.  We  call 
these  eddy  or  Foucault  currents.  They  are  particularly  preva- 
lent when  the  metal  in  question  is  magnetic,  that  is,  a  good  con- 
ductor for  the  magnetic  lines  of  force.  There  would  be  consider- 
able losses,  for  instance,  in  the  cooling  chambers  used  in  electrode 
furnaces,  to  cool  the  electrodes,  if  these  were  made  of  cast  iron 


60    ELECTRIC   FURNACES   IN   THE   IRON  AND    STEEL   INDUSTRY 

or  cast  steel,  as  both  of  these  materials  carry  the  magnetic  flux 
better  than  air.  We  are,  therefore,  obliged  to  make  these  cooling 
chambers  out  of  copper,  red  brass,  or  manganese  steel,  as  these 
materials  are  non-magnetic. 

Another  method  used  to  lessen  these  eddy  current  losses, 
is  to  greatly  subdivide  the  metallic  parts  in  which  these  eddy 
currents  might  appear.  Transformer  and  dynamo  armature 
cores  are  examples.  These  cores  are  built  up  of  sheets  as  thin  as 
.5  and  sometimes  only  .3  mm.  (.02  to  .012  inch). 

Finally  we  might  also  have  the  case  where  a  good  magnetic 
conductor,  one  of  low  magnetic  reluctance,  entirely  surrounds  an 
electric  conductor.  If  the  magnetic  conductor  should  have  a 
considerable  cross-section,  then  certain  power  losses  arise,  due  to 
the  constant  demagnetizing  influence  of  the  alternating  current. 
This  loss  is  known  as  the  hysteresis  loss.  For  this  reason,  there- 
fore, we  also  avoid  surrounding  electrical  conductors  with  good 
magnetic  conductors  in  electric  furnace  construction. 

It  seems  well  to  mention  that  besides  single  phase  alternating 
current,  polyphase  (2  or  3  phase)  alternating  current  is  more  often 
used  to  operate  electric  furnaces.  In  order  to  understand  these 
power  circuits,  we  will  add  the  following: 

Three  phase  current  is  visually  distinguishable  by  having 
three  lines  which  conduct  the  current  from  the  source  of  supply  to 
the  apparatus  using  it.  •  Whereas  with  single  phase  current  there 
are  only  two  lines,  one  line  to  lead  the  current  to  the  destination 
and  one  return  wire. 

As  the  name  three  phase  implies,  we  use  three  conductors 
and  handle  three  currents  in  this  power  transmission.  The 
vector  diagram  shows  us  this  the  plainest,  i.e.,  the  relations  be- 
tween these  currents  and  what  the  relations  are  between  the 
different  values  occurring  in  three  phase  power  transmission. 

Fig.  33  shows  us  three  vectors  which  are  separated  1 20°  from 
each  other.  These  vectors  indicate  the  direction  of  the  current 
as  they  are  actually  generated  in  3-phase  machines  and  actually 
consumed  in  3-phase  apparatus.  If  we  add  these  currents 
geometrically,  as  shown  in  the  figure,  we  observe  that  the  geomet- 


POWER  FACTOR  (COS  0)  AND  ALTERNATING  CURRENT  THEORY   61 

rical  resultant  of   two  current  forces   always  equals  the  third 
current.    This  explains  why  only  three  lines  are  necessary  to 


FIG.  34. 

conduct  a  3-phase  current,  of  which  the  third  conductor  may  be 
looked  upon  as  a  return  wire  for  the  other  two.  This  presupposes 
of  course  that  the  current  in  each  direction  or  phase  is  of  the  same 
value. 


62      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  coils  of  the  generator  or  those  of  the  power  consuming 
apparatus  which  are  built  for  3-phase  current,  may  be  connected 


FIG.  350. 


FIG.  36. 


in  two  different  ways  with  each  other.  Fig.  34  shows  the  so- 
called  Star  or  Y  connection,  in  which  the  ends  of  the  coils  of  the 
generating  or  receiving  apparatus  are  connected  together  at  the 


POWER  FACTOR  (COS  </>)  AND  ALTERNATING  CURRENT  THEORY   63 

neutral  point  A,  whereas  Fig.  35  shows  the  so-called  Delta  con- 
nection in  which  the  single  coils  are  connected  in  series,  and  the 
connecting  points  of  the  coils  are  led  off  to  the  power  mains. 

With  the  Star  or  Y  connection  we  may  have  either  the  volt- 
age of  one  phase  or  the  resultant  voltage  of  two  of  the  phases. 
The  first  is  the  potential  between  the  neutral  point  A,  Fig.  34, 
and  the  end  of  one  generator  coil,  as  shown  by  the  connections 
Aa  =  Aaz  =  Aaz  =  E.  The  other  voltage  is  the  resultant  of 
two  of  these  coils  and  is  across  the  points  a  a^,  Oz  a3,  a3  a,  and  this 
resultant  voltage  is  designated  by  e.  If  in  these  Star  connections 
the  phase  voltages  should  be  different,  there  would  however  be 
no  difference  between  the  currents  flowing  in  the  generator  coils 
and  on  the  line.  If  /  =  generator  phase  current,  and  i  =  line 
current,  then  I  =  i,  as  is  evident  by  consulting  Fig.  34. 

If  we,  however,  view  Fig.  35,  we  instantly  perceive  that  the 
phase  voltage  and  line  voltage  are  equal  to  each  other  or  E  =  e. 
On  the  other  hand  we  have  different  values  for  the  current  per 
phase  and  the  line  current.  With  3-phase  currents  for  electric 
furnaces  the  Y  connection  is  mostly  used.  What  is  the  relation 
between  these  two  voltages? 

If  we  have  the  phase  voltage  £,  we  may  obtain  the  resultant 
voltage  by  taking  the  geometric  difference  between  any  2  phase 

voltages.  If  we  refer  to  Fig.  36  we  see  that,  sin  60°  =—  E  and 
therefore  the  resultant  voltage 

e  =  2  E  sin  60° 
=  \/3  E  =  1.73  E. 

In  the  same  way  it  may  be  shown  for  A   connection  that 


These  relations  must  be  known  in  order  to  clearly  understand 
the  power  in  3-phase  circuits.  We  can  imagine  the  3-phase 
power  being  equal  to  the  sum  of  power  of  the  3  single  phases. 

We  then  obtain, 

p  =  EI  /i  cos  0  +  Ez  h  cos  <j>  +  Ez  h  cos  <f> 
and  as  we  assume  that  the  separate  phases  are  balanced  or  equally 


64   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

loaded  we  may  write  that 

p  =  3  E  I  cos  <£. 

We  saw  for   the  Y  connection  that  e  =  \/3  E  and  i  =  I. 
If  we  substitute  these  values  in  the  power  equation,  we  have 

e 
p  =  3  —  —=  .i  cos  <f>  =  v$e  i  cos  $ 

i.e.,  we  obtain  the  power  in  a  3-phase  circuit  by  multiplying  the 
current  by  the  voltage  by  the  power  factor  and  the  product  by 

V*'  . 

Finally,  it  may  be  said  that  we  have  wattmeters  which  meas- 

ure the  total  power,  p  =  \/3  e  i  cos  <j>  in  3  phase  circuits.     It  is 
therefore  an  easy  matter  to  determine  the  power  factor  in  a  3- 
phase  circuit,  provided  other  instruments  give  the  values  of  the 
current  and  voltage  of  the  3  balanced  phases. 
We  therefore  have 


In  the  above  p  =  total  power  in  either  a  Y  or  A  connection  circuit 
as  measured  by  a  wattmeter,  i  =  the  current  in  each  line, 
sometimes  only  measured  by  one  ammeter,  and  e  =  voltage  as 
measured  by  the  usual  a.c.  voltmeter. 


CHAPTER  V 

GENERAL  CONDITIONS  FOR  THE  OPERATION  OF 
ELECTRIC   FURNACES 

BEFORE  we  deal  with  the  furnace  designs  now  largely  used 
for  steel  making,  it  may  be  well  to  discuss  a  few  general  questions. 
An  understanding  of  these  is  of  great  importance  in  order  that 
we  may  correctly  judge  an  electric  furnace. 

First  and  foremost  the  question  arises: 

Why  has  the  steel  industry  in  general  an  interest  in  electric 
furnaces,  and  what  advantages  does  the  electric  furnace  offer 
compared  to  the  existing  metallurgical  apparatus? 

It  is  obvious  that  the  advantages  will  have  to  be  of  some 
moment,  if  the  iron  masters  are  to  discard  or  supplement  their 
hitherto  satisfactory  methods  of  procedure. 

It  behooves  us  then  to  consider  first  the  proved  and  peculiar 
heating  effects  derived  entirely  from  electricity.  We  find  the 
following  characteristics : 

1 .  The  use  of  electricity  as  a  heating  agent  makes  an  extraor- 
dinary and  quick  heat  possible,  which  same  is  impossible  with 
any  system  of  gas  heating.     Here  it  may  be  noted,  that  before  the 
introduction  of  the  electric  furnace  into  the  steel  industry,  it 
was  only  possible  to  make  refractories  stand  temperatures  of 
2000°  C.,  whereas  we  may  now  reach  any  temperature  up  to 
3500°  C.  in  the  electric  furnace. 

2.  With  the  aid  of  electrical  control  the  heat  can  be  regulated 
most  accurately,  so  that  the  charge  can  be  brought  to  any  de- 
sired temperature  and  kept  there,  according  to  the  demands  of 
the  process  in  question. 

3.  Electricity  offers  us  the  cleanest  heating  agent  imaginable, 
so  that  we  are  enabled  to  avoid  all  deleterious  influence  -which 
other  heating  agents  have;  for  electric  furnaces  allow  us  to  oper- 
ate in  any  atmosphere,  and  this  prevents  reactions  taking  place 

66 


66    ELECTRIC   FURNACES   IN   THE   IRON   AND    STEEL   INDUSTRY 

which  may  be  caused  by  atmospheric  elements,  gases,  or  the 
products  of  combustion. 

4.  The  characteristics  noted,  in  sections  i  and  3,  allow  the 
steel  bath  to  be  refined  to  any  high  degree.    Sulphur  particularly 
may  be  entirely  eliminated,  so- that  a  high  class  finished  product 
may  be  made  from  impure  and  cheap  raw  material. 

5.  The  electric  furnace  allows  us  to  make  crucible  quality  steel 
in  large  quantities  (as  mentioned  in  section  4),  made  from  cheap 
raw  material,  and  yet,  at  the  same  time,  it  turns  out  a  completely 
homogeneous  product.    This  product  has  hitherto  been  possible 
only  in  the  crucible  furnace,  where  many  separate  crucibles  are 
used,  charged  with  the  purest  and  most  expensive  of  raw  materials. 

6.  In  many  cases  the  product  of  electric  furnaces  shows  cru- 
cible quality  characteristics,  even  though  the  cheapest  metal  had 
been  charged.    This  high  quality  cannot  be  achieved  in  any  other 
type  of  furnace.     The  reason  for  this  being  that  the  heating  agent 
does  not  in  any  way  influence  the  charge  and  therefore  the  steel 
may  stay  in  the  electric  furnace  as  long  as  deemed  best,  and  held  at 
any  desirable  temperature,  mean  while  allowing  the  gases  to  escape. 

7.  The  saving  in  the  additions  of  ferro  alloys  is  another 
important   consideration,    the   use   of     ferromanganese,   ferro- 
silicon,  etc.,  being  considerably  reduced — one-third  to  one-half 
less  ferromanganese — even  when  added  cold.    When  electrically 
melted  ferromanganese  is  added  to  electric  steel,  the  saving  is 
still  greater,  and  of  the  greatest  importance  for  quantity  pro- 
duction, as  the  second  grade  material  is  considerably  reduced. 

As  these  are  the  general  principles  which  make  the  electric  fur- 
nace valuable  to  the  steel  industry,  it  seems  advisable  to  state  the 
requirements  which  an  ideal  electric  furnace  would  demand  in 
order  that  the  above  advantages  may  be  best  attained.  Particu- 
larly as  the  numoer  of  different  furnace  designs  are  -numerous. 

Surely  everybody  who  is  confronted  with  the  question  of 
installing  an  electric  furnace,  will  see  first  that  the  installations 
shall  cost  the  least  amount  of  money,  and  second  that  the  type 
used  combines  the  greatest  simplicity  with  the  greatest  safety 
during  operation. 

The  requirements,  therefore,  should  be  as  follows: 


GENERAL   CONDITIONS  67 

1.  The  ability  to  use  any  prevailing  alternating  current  at 
any  voltage  and  frequency. 

2.  The  avoidance  of  any  suaaen  changes  in  the  load 

3.  Ease  of  regulating  the  incoming  current. 

4.  High  electrical  efficiency. 
To  which  are  added  the  following: 

5.  A  furnace  of  the  tilting  variety. 

6.  Easily  surveyed  and  accessible  hearth. 

7.  The  electrical  heating  or  any  of  its  necessary  auxiliaries 
must  in  no  way  influence  the  chemical  composition  of  the  steel 
or  the  slag. 

8.  The  ability  to  reach  any  desired  uniform  temperature  in 
all  parts  of  the  bath,  and  at  the  same  time  avoiding  any  local 
under-  or  over-heating. 

9.  The  furnace  should  be  as  versatile  in  its  application  as 
possible.     These  requirements  further  stipulate  the  following: 

10.  Equally  advantageous,  rapid,  and  inexpensive  methods  of 
removing  all  impurities  contained  in  the  charge,  notably  sulphur 
and  phosphorus,  and  furthermore : 

11.  The  possibility  of  completely  and  easily  removing  any 
slag  in  the  furnace,  and  of  being  quickly  and  easily  able  to 
renew  it. 

12.  Complete  uniformity  of  the  material  in  all  parts  of  the 
molten  metal  and  consequently  a  sufficient  circulation  in  the  bath. 

13.  Avoidance  of  too  much  agitation  in  the  bath,  and  there- 
fore providing  an  advantageous  standing  of  the  metal. 

14.  The  possibility  of  providing  various  furnace  sizes,  which 
would  have  to  fit  prevailing  conditions. 

15.  The  highest  possible  thermal  efficiency  with  all  furnace 
sizes. 

1 6.  The  avoidance  of  all  water  cooling. 

17.  The  least  possible  refractory  and  initial  cost  and  low- 
operating  cost. 

18.  The  possibility  to  melt  cold  scrap  economically. 

19.  And  for  foundry  purposes,  the  ready  adaptability  of  the 
furnace  to  intermittent  service. 

It  may  be  again  remarked  that  the  above  requirements  are 


68    ELECTRIC   FURNACES   IN   THE   IRON  AND   STEEL  INDUSTRY 

those  which  would  be  expected  of  an  ideal  furnace.  The  furnaces 
discussed  in  the  following  chapters  are  those  in  practical  use  and 
therefore  only  partly  fulfill  the  above  requirements,  some  more 
and  some  less,  so  that  the  exactions  made  of  an  ideal  furnace 
only  serve  as  a  normal  estimate,  with  which  the  following  various 
designs  are  compared. 

First  of  all,  though,  it  seems  necessary  to  dwell  more  in- 
timately upon  the  importance  of  several  points. 

i.  Of  the  furnace  operation  we  required  the  use  of  any  pre- 
vailing current.  • 

If  this  requirement  were  fulfilled  it  would  enable  any  electric 
furnace  to  be  connected  to  an  existing  central  station,  no  matter 
if  this  were  a  city  electric  plant  or  the  works'  own  isolated 
station.  If  the  electrical  power  was  sufficient  in  either  case, 
only  the  connection  to  the  furnace  installation  and  the  latter 
itself  would  be  necessary,  so  that  the  expense  of  a  special  genera- 
tor, which  would  only  be  ordered  for  the  furnace  itself,  would  be 
saved. 

If,  on  the  other  hand,  the  case  should  present  itself  where  the 
available  power  of  an  existing  isolated  plant  was  entirely  in  de- 
mand for  other  purposes,  then  in  this  case  it  would  also  be 
advantageous  if  any  available  current  could  be  used  for  the 
electric  furnace,  so  that  the  generator  installation  furnished  for 
the  electric  furnace  could  at  the  same  time  and  in  any  event  be 
used  as  a  reserve  for  the  remaining  generators;  or  the  generators 
would  act  as  a  mutual  reserve,  as  well  for  the  main  generator 
installation  as  for  furnace  generators,  which  would  then  insure 
the  best  service  conditions. 

If  the  consumer  of  electric  current  does  not  have  to  take 
into  consideration  the  conditions  existing  in  a  distant  central 
station  when  connecting  to  its  lines,  then  such  a  connection  also 
offers  important  advantages  as  it  enables  the  existing  central 
station  current  to  be  used.  Furthermore  the  furnace  installation 
in  this  case  can  easily  be  erected  in  a  comparatively  small  place, 
besides  saving  the  attendance  for  one's  own  power  plant,  or  that 
required  for  a  rotary  transformer.  This  is  entirely  independ- 
ent of  the  fact  that  small  works  are  hardly  able  to  generate  power 


GENERAL  CONDITIONS  69 

as  cheaply  as  it  can  be  sold  by  large  central  stations,  except- 
ing when  high  pressure  internal  combustion  oil-engines  are  used. 

Accordingly,  it  would  be  desirable,  of  course,  if  direct  or 
continuous  current  could  be  used  for  operating  electric  furnaces, 
in  case  a  steel  mill  only  possessed  a  direct  current  power  plant. 
We,  however,  saw  in  the  third  chapter  that  on  account  of  the 
chemical  action  of  direct  current,  this  does  not  appear  suitable 
for  operating  electric  furnaces,  and  as  direct  current  can  only  be 
changed  from  a  higher  to  a  lower  voltage,  such  as  is  used  for 
arc  furnaces,  by  means  of  expensive  rotary  converters,  consisting 
of  driving-motor  and  gerierator,  and  if  the  continuous  current 
were  to  be  used  directly  from  a  low  voltage  plant,  the  cost  of 
the  connecting  wires  and  cables  would  be  extraordinarily  .ex- 
pensive, as  the  distances  are  usually  considerable;  therefore, 
direct  current  is  practically  never  used  today  for  any  electric 
furnaces  in  the  iron  industry.  If,  in  spite  of  this,  we  see  the 
assertion  made  here  and  there  in  advertising  mediums,  that  a 
furnace  may  also  be  operated  with  direct  current,  then  these 
assertions  are  to  be  approached  with  the  greatest  care,  for  when 
these  are  accurately  tested,  it  will  always  be  found  that  such 
allegations  are  misleading. 

It  can  accordingly  be  established  that  direct  current  does 
not  come  into  play  at  all  for  operating  electric  furnaces.  These 
latter  may,  however,  be  adjusted  to  any  conditions  which  are 
offered  by  the  modern  alternating  current  station. 

It  is  well  known  that  at  present  alternating  current  stations 
are  built  for  three  phase  current,  because  the  electrical  conditions 
are  especially  favorable.  When  an  electric  furnace  therefore  is 
to  be  connected  to  an  existing  power  plant,  we  shall  no  doubt, 
in  the  majority  of  cases,  find  that  it  is  to  be  connected  to  a  three 
phase  plant.  In  this  case  a  three  phase  furnace  shall  have  a 
particular  advantage  which  exactly  fits  into  the  conditions 
offered  by  an  existing  electric  station.  A  two  phase  furnace  has 
the  same  advantage  as  a  three  phase  furnace,  even  though  the 
former  is  to  be  connected  to  a  three  phase  circuit,  as  three  phase 
current  may  be  changed  to  two  phase  by  means  of  stationary 
transformers  having  the  Scott  connection.  These  transformers 


70    ELECTRIC   FURNACES   IN   THE   IRON   AND    STEEL   INDUSTRY 

are  necessary  in  such  cases  to  regulate  the  power  fed  to  the 
furnace,  i.e.,  these  regulating  and  phase  changing  transformers 
would  serve  the  double  purpose  of  simultaneously  changing 
three  to  two  phase  current  or  vice  versa,  and  regulate  the  current 
besides.  Whereas  a  single  phase  furnace  under  these  conditions 
would  necessitate  the  installation  of  a  rotary  transformer,  con- 
sisting of  a  three  phase  motor  and  a  single  phase  generator, 
which  would  considerably  increase  both  the  initial  and  the 
current  costs.  But  even  though  it  would  be  necessary  to  install 
a  new  alternator  to  deliver  current  to  the  furnace,  the  three  phase 
(or  two  phase)  furnace  has  certain  advantages.  In  this  case  it 
would  be  of  considerable  importance  to  obtain  the  least  expensive 
electric  plant  consistent  with  economic  operation.  And  it  may 
be  of  determining  importance  here  as  a  polyphase  alternator  costs 
about  25  to  33  per  cent,  less  than  a  corresponding  single  phase 
alternator,  other  things  being  equal. 

If,  on  the  other  hand,  single  phase  current  only  should  be 
available,  then  the  polyphase  furnace  would,  of  course,  be  more 
expensive,  as  the  single  phase  current  would  then  have  to  be 
changed  to  polyphase  current  by  means  of  a  rotary  transformer. 
It  appears,  therefore,  that  the  utilization  of  any  existing  single 
phase  current  would  be  of  particular  advantage. 

It  seems  that  being  able  to  use  any  voltage  is  of  lesser  im- 
portance. For  as  our  requirements  have  limited  us  to  the  use 
of  alternating  currents,  there  no  longer  remains  any  noteworthy 
difficulty  in  changing  or  transforming  a  high  central  station 
voltage  to  a  lower  furnace  voltage.  For  this  change  can  be  made 
very  simply,  and  almost  without  loss,  by  means  of  stationary 
transformers,  which  only  entail  a  comparatively  small  expense 
and  almost  possess  an  unlimited  life. 

Contrary  to  the  foregoing,  we  find  that  it  is  of  great  im- 
portance to  be  able  to  use  any  existing  frequency  for  the  electric 
furnace.  Unfortunately,  this  requirement  is  not  yet  completely 
fulfilled  by  all  of  the  well-known  furnace  designs.  Among 
others,  the  main  reason  is  to  be  found  in  the  power  factor  or 
cos  <£  falling  as  the  frequency  rises.  (See  Chap.  4.) 

It  can,  therefore,  only  be  established,  (taking  into  considera- 


GENERAL   CONDITIONS  71 

tion  that  only  the  practically  attainable  can  be  asked,)  that  an 
electric  furnace  should  be  operated  with  normal  frequencies, 
meaning  thereby  15,  25,  50  and  60  cycles. 

In  order,  however,  to  point  out  early,  of  what  importance 
the  frequency  of  an  alternator  is  as  regards  cost,  it  may  be  men- 
tioned that  the  costs  of  a  single  phase  alternator  of  25  cycles  and 
a  similar  one  of  equal  capacity,  but  of  only  five  cycles,  will  bear 
the  ratio  of  i  :  2.  These  figures  may  perhaps  best  show,  charac- 
teristically, the  influence  of  abnormally  low  frequencies. 

We  now  come  to  the  second  requirement,  viz.:  the  avoidance 
of  all  sudden  and  untoward  changes  in  the  load. 

That  such  load  changes  and  principally  current  fluctuations  are 
of  the  greatest  disadvantage  to  every  electrical  power  plant,  needs 
no  explanation.  It  may  only  be  remarked  here  that  no  city  light- 
ing and  power  plant  would  allow  an  electric  furnace  on  its  lines, 
which  operated  with  heavy  power  fluctuations,  without  first  inter- 
posing a  rotary  transformer  with  suitably  heavy  fly-wheels  or 
other  appurtenances  which  would  be  able  to  absorb  these  fluctua- 
tions and  thus  keep  them  away  from  the  central  station.  This 
same  requirement  would  also  have  to  be  met  with  in  every  other 
isolated  plant,  if  any  value  is  placed  on  its  economical  operation. 

With  interposed  rotary  transformers,  therefore,  the  power 
fluctuations  would  increase  the  initial  cost.  This  also  holds, 
provided  the  furnace  is  connected  to  a  special  generator.  For 
it  is  evident  that  the  generator  must  stand  the  greatest  current 
fluctuations  without  injury,  i.e.,  the  generator  must  be  built  for 
much  higher  currents  than  if  there  were  no  irregular  power  surges. 
In  other  words,  a  generator  required  to  operate  a  furnace,  having 
current  fluctuations,  could  operate  a  much  larger  furnace  which 
was  free  from  such  fluctuations.  To  this  must  be  added  the 
fact  that  the  generator's  prime  mover  would  run  under  much 
more  unfavorable  conditions,  and  with  a  much  poorer  efficiency, 
if  the  current  surges  are  to  be  overcome,  than  if  it  only  had  to 
deliver  the  power  uniformly  or  at  a  gradually  changing  rate. 
The  power  delivered  to  an  electric  furnace,  having  power  fluctua- 
tions, is  similar  to  that  taken  by  an  electrically  driven  rolling 
mill  or  by  an  electric  railway. 


72    ELECTRIC   FURNACES   IN   THE   IRON  AND   STEEL   INDUSTRY 

In  order  to  give  an  arithmetical  example,  it  may  be  said  that 
normally  turbo-generators  have  a  steam  consumption  of  7.5  kg. 
per  kw.-hr.  (16.5  Ibs.  per  kw.-hr.),  whereas  turbo-generators  for 
railway  service,  with  their  required  overload  capacity,  often  have 
a  steam  consumption  of  8. 25  (18.15)  and  more  up  to  10  kg.  per 
kw.-hr.  (22  Ibs.).  These  figures  about  give  a  correct  idea  of  the 
advantage  which  an  electric  furnace  has  whose  operating  force 
is  free  from  fluctuations.  This  is  quite  apart  from  having  a 
less  expensive  power  plant  which  a  smooth  running  furnace 
has.  Furthermore,  a  power  plant  subject  to  having  power 
fluctuations,  is  naturally  liable  to  much  greater  wear  than  is 
occasioned  by  uniformly  loaded  machines. 

To  the  third  point,  viz.:  the  ease  of 'regulating  the  electric  fur- 
nace so  as  to  give  higher  or  lower  temperatures,  nothing  more  can 
be  added.  This  is  fulfilled  as  the  furnace  voltage  can  be  easily 
changed,  by  suitable  electrical  apparatus,  so  that  this  require- 
ment is  fulfilled  by  all  furnaces  in  the  same  way. 

Likewise  the  fourth  point  leaves  nothing  to  be  said  regarding 
the  requirement  for  a  furnace  with  the  highest  possible  efficiency. 
For,  it  is  self-evident  that  a  poor  efficiency  would  entail  a  greater 
power  absorption  for  the  same  work,  and  thereby  the  operating 
costs  might  be  considerably  increased. 

The  remaining  requirements  refer  mainly  to  metallurgical 
facts,  which  are  discussed  in  detail  in  the  second  part  of  this 
book.  That  is  why  they  are  only  given  here  just  sufficiently  to 
enable  one  to  judge  the  different  electric  furnace  designs. 

As  a  comparatively  great  number  of  charges  are  treated  in  an 
electric  furnace,  especially  when  operating  with  hot  metal, 
nearly  all  the  furnaces  in  practical  operation  to-day  are  made  of 
the  tilting  variety.  For  this  allows  the  teeming  to  be  accom- 
plished with  greater  ease,  and  avoids  much  trouble  caused  by 
the  giving  away  of  the  tapping  hole.  Consequently  the  demand 
for  tilting  furnaces  today  is  a  general  one. 

In  like  manner  there  is  recognized  the  demand  for  an  easily 
surveyed  and  accessible  hearth.  -  For,  every  metallurgical 
operation  will  be  placed  in  jeopardy  without  it.  Therefore 
electric  furnaces  should  have  working  doors  placed  at  moderate 


GENERAL   CONDITIONS  73 

heights  above  the  bath,  a  little  to  one  side,  from  which  it  should 
be  possible  to  see  the  entire  hearth.  This  may  be  required,  for 
instance,  in  order  to  exactly  determine  the  condition  of  the  slag, 
or  to  be  convinced  when  changing  them,  that  the  bath  is  really 
free  therefrom  before  endeavoring  to  make  a  new  slag.  This  is 
entirely  independent  of  the  fact  that  side  doors  are  by  far  the 
most  advantageous  and  convenient  for  charging  slag.  On 
account  of  the  absence  of  an  easily  surveyed  hearth,  such  resist- 
ance furnaces  as  described  in  the  third  chapter,  having  channels 
running  to  and  fro,  are  absolutely  to  be  discarded. 

It  seems  self-evident  that  we  should  expect  an  electric  furnace 
to  have  its  heat,  or  the  necessary  appliances  required  to  give  it, 
without  influence  on  the  chemical  composition  of  the  steel  or 
slag.  For  it  is  just  by  these  means  that  the  electric  furnace  is 
to  prove  its  superiority  over  the  older  gas-heating  type.  This 
point  is,  therefore,  to  be  borne  well  in  mind  with  every  different 
furnace  design.  .For  suppose  we  assume  that  at  any  time 
during  the  metallurgical  process,  for  instance,  during  the  oxida- 
tion period,  the  electrical  heating  should  in  any  way  favor 
the  oxidation,  then  this  electrical  heat  effect  would  also  be 
present  at  any  other  time,  i.e.,  during  the  reducing  period,  and 
the  furnace  would  then  consequently  be  working  at  a  disadvant- 
age. Thus  the  harm  of  these  effects  is  often  greater  than  the 
good  they  do,  as  they  are  also  present  when  they  are  not 
wanted. 

Every  metallurgist  will  concede  that  it  is  justifiable  to  expect 
an  electric  furnace  to  reach  any  desired  temperature  and  still 
avoid  any  over-  or  under-heating.  That  primarily  every  practi- 
cally desired  temperature  must  be  attainable  is  evident,  when 
we  consider  that  the  electric  furnace  must  enable  us  to  reach 
the  most  advantageous  temperature  for  every  stage  of  the 
metallurgical  process.  This  requirement,  therefore,  falls  to- 
gether with  the  one  requiring  an  easy  regulation  of  the  incoming 
energy.  With  all  this,  it  is  of  particular  importance  that  the 
entire  furnace  contents  be  heated  uniformly,  so  that  over-  and 
under-heating  is  not  to  be  feared;  it  is  much  more  likely  that 
there  would  be  an  over-heating.  The  former  of  these  is  hardly 


74    ELECTRIC   FURNACES   IN   THE    IRON   AND    STEEL   INDUSTRY 

likely  to  occur  in  case  considerable  heat  is  carried  away  by 
the  water-cooled  appliances  in  connection  with  the  electrodes. 
Borchers,  in  his  1898  address  before  the  "Verein  deutscher 
Eisenhiittenleute, ' '  said : 

"As  a  matter  of  fact  we  need  not  fear  that  we  cannot  reach 
almost  any  temperature  by  electrical  means  for  this  or  that 
purpose,  for  we  shall  have  to  place  much  greater  weight  on 
guarding  against  wastefulness  on  account  of  working  with  too 
high  temperatures." 

The  ninth  point  requires  the  electric  furnace  to  be  as  versatile 
in  its  application  as  possible,  and  thereby  possess  the  greatest 
adaptability  in  order  to  work  it  in  conjunction  with  present  or 
future  processes.  It  goes  without  saying  that  it  would  be  par- 
ticularly advantageous  for  the  electric  furnace,  if  it  were  possible 
to  make  in  it  the  greatest  variety  of  steel,  equally  well  and 
economically,  and  of  the  same  good  quality.  For  even  though 
one  or  the  other  object  of  making  the  steel  may  primarily  be  the 
absolutely  determining  factor,  it  is  still  to  be  noted  that  the 
electric  furnace  has  a  far-reaching  application  even  today. 
However,  there  are  at  present  still  many  new  fields  open  to  its 
product.  So  that  even  though  it  does  not  appear  to  be  absolutely 
necessary,  still  by  far  in  the  most  cases  it  would  appear  to  be 
advantageous,  provided  a  qualified  electric  furnace,  or  some 
chosen  system,  fits  into  the  working  program  equally  well  for 
the  reception  of  a  new  quality,  as  the  previous  material  did. 

The  further  requirements  from  the  zoth  to  the  i4th  are  self- 
evident,  if  the  previous  demands  made  upon  the  electric  furnace 
are  to  be  fulfilled.  As  the  principal  advantage  of  the  electric 
furnace  lies  in  the  fact  that  it  can  turn  out  the  highest  quality 
steel  from  the  cheapest  raw  material,  it  must  consequently  be 
easy  to  attain  the  removal  of  the  impurities  contained  in  the 
charge,  provided  the  electric  furnace  economically  permits  what- 
ever refining  there  may  be  to  do.  First,  we  shall  have  to  concern 
ourselves  with  the  entire  elimination  of  the  phosphorus  and 
sulphur;  while  removing  the  impurities  which  alloy  themselves 
with  the  iron,  (such  as  copper,  for  instance,)  is  also  thus  so  far 
impossible  in  the  electric  furnace.  If  all  the  refining  possible  is 


GENERAL  CONDITIONS  75 

to  be  carried  out,  it  is  absolutely  necessary  that  the  slag  for  re- 
moving the  phosphorus,  for  instance,  can  be  completely  removed 
from  the  furnace.  For  otherwise,  when*  the  metallurgical  proc- 
ess is  continued  for  the  removal  of  other  impurities  previously 
taken  up  by  the  slag,  the  phosphorus  will  again  be  taken  up  by 
the  molten  metal.  The  requirement  of  being  able  to  completely 
remove  slag  from  the  furnace  is  covered,  therefore,  by  doors 
enabling  us  to  have  an  easily  surveyed  and  accessible  hearth. 

It  seems  just  as  self-evident  that  the  impurities  be  removed 
from  all  parts  of  the  bath,  as  it  is  necessary  that  all  alloys  added 
to  it  are  absorbed  equally  by  all  parts  of  it.  Otherwise  an  un- 
even material  would  result.  On  this  account,  therefore,  a  good 
electric  furnace  has  to  have  an  adequate  circulation,  which  assures 
the  greatest  uniformity  of  material  in  all  parts  of  the  hearth. 
The  desired  agitation,  however,  must  not  exceed  certain  limits, 
as  otherwise  the  advantage  of  the  electric  furnace  would  not  be 
used  which  allows  any  slag  solutions  to  be  separated  from  the 
furnace  contents. 

Finally,  in  order  that  the  furnace  can  have  a  far-reaching 
application,  it  is  necessary  that  the  furnace  be  built  of  such  sizes 
which  seem  to  best  fit  present  or  future  installations.  This  is 
to  be  kept  in  mind,  for  instance,  when  the  furnace  is  to  operate 
as  an  adjunct  to  a  converter  or  an  open  hearth  plant.  In  such 
cases,  it  is,  of  course,  advantageous,  if  the  furnace  can  receive  a 
whole  charge  from  a  converter.  It  is  such  reasons  as  these  that 
make  it  desirable  to  build  furnaces  of  the  largest  capacity. 

The  1 5th  requirement  exacted  a  high  thermal  efficiency,  and 
no  explanation  of  this  is  necessary.  However  a  few  words  may 
be  said  regarding  the  possible  influence  of  using  water  cooling. 
First  of  all,  it  is  evident  that  energy  losses  are  caused  by  every 
cooling  means,  and  water  cooling  aids  this  in  the  strongest  degree, 
thus  lowering  the  efficiency.  Water  cooling  may  become  partic- 
ularly harmful  when  it  is  used  in  such  manner  as  to  considerably 
cool  those  wall  parts  which  encircle  the  molten  metal.  For 
then  the  danger  arises  of  the  fluid  iron  assuming  a  certain  tough 
fluidity,  at  these  places,  which  makes  it  very  hard  to  obtain  a 
uniform  composition  of  the  entire  furnace  contents.  Finally 


76    ELECTRIC   FURNACES   IN   THE   IRON   AND   STEEL   INDUSTRY 

the  employment  of  water  cooling  may  easily  cause  dangerous 
explosions  if  the  devices  used  are  not  very  well  -protected.  If 
the  water  cooling  is  beneath  the  bath  and  the  molten  metal 
runs  into  it  an  explosion  will  occur,  but  it  is  much  less  dangerous 
if  the  water  cooling  is  above  the  bath,  i.e.,  where  the  water  would 
run  into  the  melted  charge. 

It  only  remains  to  mention  the  last  requirements  consisting 
of  the  lowest  installation  costs,  likewise  the  lowest  refactory 
cost,  and  thereby  the  lowest  operating  cost  which  brings  together 
nearly  all  the  exactions  which  an  ideal  furnace  has  to  fulfill. 
Commercial  intermittent  operation  is  also  a  requirement  to 
which  a  furnace  should  be  adaptable  without  badly  or  completely 
cracking  or  checking  the  bottom,  side  walls,  or  roof  refractories, 
even  though  this  demand  is  more  often  made,  or  almost  ex- 
clusively so  in  foundries  compared  to  steel  mills,  where  in  the 
former  it  is  usual  to  operate  only  during  the  day.  It  affects  the 
smaller  furnaces  considerably  more  than  the  larger  ones,  as 
furnaces  of  larger  than  5  to  6  tons  per  heat  have  so  far  not  been 
adopted  in  foundries,  but  are  more  often  from  i  to  3  tons  in 
size  per  heat.  Lastly,  the  commercial  ability  to  melt  cold  scrap 
is  important,  and  this  feature  is  apparent  with  all  arc  furnaces, 
but  with  induction  furnaces  where  comparatively  much  metal 
must  remain  in  the  hearth  to  facilitate  the  making  of  the  suc- 
ceeding charge,  cold  metal  charging  only,  has  been  found  to  be 
too  costly.  That  is  why  induction  furnaces  to-day  are  used 
mainly  for  liquid  charges,  or  for  mixed  hot  and  cold  metal. 
Unfortunately,  the  complete  attainment  of  this  ideal  has  so  far 
not  been  accomplished  by  actual  practice,  as  evinced  by  electric 
furnace  construction.  This  will  be  considered  in  the  following 
chapters,  where  the  constructions,  as  used,  are  compared  with 
the  stipulated  requirements.  We  will  find  there,  that  every 
furnace  design  has  certain  advantages,  but  also  certain  disadvan- 
tages compared  with  every  other  electric  furnace  design.  And  it 
is  this  which  makes  the  choice  of  a  furnace  thus  far  so  difficult, 
for  practical  experience  and  the  race  in  the  open  market  have  not 
yet  perceptibly  proved  the  superiority  of  one  or  another  furnace 
system. 


CHAPTER  VI 

ARC  FURNACES  IN  GENERAL 
THE  ARC 

IF  the  ends  of  two  current  carrying  wires  are  brought  together 
so  that  the  current  may  flow,  and  if  the  two  ends  are  then  slightly 
separated,  no  interruption  of  the  current  will  take  place.  But 
there  will  appear  a  small,  highly  luminous  flame  between  the 
ends  of  the  wires,  which  takes  the  place  of  the  conductor  at  the 
point  of  interruption.  With  this,  then,  we  have  to  deal  with  an 
entirely  different  property  from  that  which  the  electric  spark 
presents.  The  latter  also  represents  a  current  transference 
through  the  air.  But  far  higher  voltages  are  necessary  for  the 
production  of  a  spark  than  the  arc  calls  for,  an  example  of  which 
we  have  just  given  above.  In  the  latter,  it  is  not  the  air  which 
bridges  the  current,  but  the  gases  emanating  from  the  metal  of 
the  wires  between  which  the  arc  has  been  struck.  The  way  the 
arc  occurs  then  is  as  follows: 

At  the  instant  when  the  ends  of  the  two  wires  are  separated, 
a  rise  of  resistance  of  such  magnitude  appears  at  the  point  of 
separation,  that,  with  the  current  flow,  a  corresponding  and  im- 
portant heating  effect  takes  place.  It  is  under  this  influence 
that  the  metal  evaporates  at  the  points  of  contact.  If  the 
separation  should  be  increased,  then  the  distance  between  the 
wire  ends  becomes  so  filled  with  metallic  gases,  that  these  now 
take  up  the  current  transference  at  the  point  of  interruption. 
The  metallic  gases,  however,  are  much  poorer  conductors  than 
the  metal  itself.  It  follows  then  that  the  current  in  its  path, 
from  the  end  of  one  wire  to  the  other,  has  to  overcome  consider- 
able resistance.  The  current  flowing  through  this  resistance 
gap  generates  such  high  temperatures,  that  more  metal  is  gasified 
at  the  gap,  in  this  way  maintaining  the  arc.  If  no  provisions 
have  been  made  for  hand  or  automatic  regulation  which  keeps 
the  distances  between  the  wire  ends  constant,  then  the  arc  will 

77 


78     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

rupture  itself.  This  will  happen  as  soon  as  the  distance  between 
the  rigid  wires  is  so  large  that  the  potential  provided  is  no  longer 
great  enough  to  overcome  the  resistance  of  the  arc.  Should  the 
arc  be  interrupted  and  it  is  desired  to  create  it  again,  then  the 
same  ends  of  the  wire  must  be  brought  together  again,  so  that 
the  arc  may  again  be  struck. 

It  may  be  noticed,  when  striking  an  arc,  that  the  metallic 
gases  of  the  positive  wire  end  or  anode  are  carried  away  violently. 
This  keeps  the  metallic  gases  together  in  a  comparatively  con- 
tracted area,  thus  making  a  definite  path  for  the  current. 

Even  though  the  conducting  metallic  gas  stream  heated  as  a 
resistance  between  the  electrodes  is  absolutely  necessary  in 
order  to  maintain  the  arc,  it  can  be  interrupted  by  thrusting  a 
cold  body  into  the  arc  stream,  although  the  maintenance  of  the 
arc  is  being  upheld  by  an  entirely  permissible  distance.  When 
the  arc  is  broken  a  decided  cooling  off  then  occurs  at  the  point 
of  interruption.  This  phenomenon  is  also  to  be  considered  with 
the  operation  of  arc  furnaces. 

From  the  above  it  is  evident  that  every  arc  furnace  furnishes 
that  temperature  which  is  required  to  gasify  the  conductors 
between  which  the  arc  is  to  be  made.  For  the  gasification  of  the 
conductor  ends  is  the  hypothesis  upon  which  the  maintenance 
of  an  arc  rests. 

The  best  known  arc  formation  is  that  which  we  see  in  the 
ordinary  arc  lamp.  Here  the  arc  is  usually  made  between  two 
carbon  electrodes. 

The  arcs  in  electric  furnaces  are  made  in  a  very  similar  way, 
for  here  carbon  electrodes  are  also  used  to  form  the  arc.  As 
before  said,  this  arc  gives  a  very  high  temperature,  in  fact  the 
highest  which  has  so  far  been  reached;  for  in  the  carbon  we 
possess  the  most  resistive  to  gasification  conducting  material,  and 
this  gasifies  at  about  3500°  C.  This  gives  us  then  the  arc  temper- 
ature with  which  iron  and  steel  baths  are  heated  in  arc  furnaces. 

Figs.  37  to  39  show  the  various  possibilities  which  may  be 
utilized  for  heating  metal  baths  by  the  electric  arc.  In  the 
schematically  shown  arrangement  of  Fig.  37  and  370,  where  the 
arc  is  formed  directly  between  two  or  three  carbon  electrodes, 


ARC  FURNACES  IN  GENERAL 


79 


we  have  the  purest  arc  heating.  The  heating  of  the  bath  takes 
place  by  means  of  the  radiating  heat  of  the  arc.  The  hearth  is 
immediately  underneath  the  arc.  These  furnaces  are  generally 
known  today  as  radiating  arc  furnaces.  The  earliest  commercial 
arc  furnace  using  this  form  of  arc  heating,  Fig.  37,  is  the  Stassano 
furnace,  while  Fig.  370  shows  the  Rennerfelt  method  of  heating. 
These  are  the  best  known  arc  furnaces  using  this  form  of  arc 
heating  which  will,  be  discussed  in  detail  in  the  next  chapters. 

Figs.  38  and  39  show  the  main  idea  of  two  other  heating 
possibilities  when  using  the  arc.  These  methods  have  the 
common  characteristic  of  the  hanging  carbon  electrode,  which 
allows  the  arc  to  impinge  itself  directly  against  the  metal.  In 
both  of  these  cases  the  metal  bath  is  part  of  the  electrical  circuit, 
so  that  theoretically  speaking  we  no  longer  have  an  exclusive 


FIG.  370. 


FIG.  37- 


FIG.  38. 


arc  heating.  For  the  charge,  composed  of  slag  and  metal, 
naturally  offers  a  certain  resistance  to  the  part  of  the  current, 
by  the  overcoming  of  which  heat  is  generated,  no  matter  what 
the  amount  may  be.  Even  though  the  resistance  heating  of 
the  metal  does  not  practically  enter  into  the  question  at  all,  the 
designation  of  calling  these  furnaces  combined  arc  and  resistance 
urnaces  is  at  least  theoretically  correct.  Nevertheless  these 
two  furnaces  have  radical  differences.  The  one  shown  by  Fig. 
38  has  the  electrodes  of  all  poles  or  phases  above  the  bath, 
whereas  with  the  furnace  shown  by  Fig.  39,  one  pole  is  above, 
the  other  is  constructed  in  a  suitable  position  below  the  bath. 
The  best  known  application  of  the  former  possibility  is  the 
Heroult  furnace,  whereas  the  equally  well  known  Girod  furnace 
embodies  the  second  qualification. 

The  question  arises,  where  does  the  real  heating  take  place, 
in  furnaces  as  shown  by  the  Figs.  38  and  39 — where  the  arcs 
impinge  directly  against  the  bath? 


80     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Although  this  question  is  discussed  in  detail  in  the  chapter 
on  the  Girod  furnace  and  an  arithmetical  example  given,  still 
the  general  answer  to  this  may  well  be  given  here,  which  Borchers 
gave  in  1905  in  an  address  before  the  "Verein  deutscher  Eisen- 
hiittenleute."  A  translation  of  this  follows: 

"When  the  electric  current  leaves  the  electrodes,  a  layer 
of  air,  gas  or  some  vapor  is  formed  between  the  electrode  and 
the  slag,  which  is  a  heat  generating  resistance  in  the  circuit. 
This,  therefore,  gives  us  the  possibility  of  arc  heating.  The 
bottom  surface  of  the  electrode  encompasses  about  1000  sq.  cm. 
(155  sq.  in.),  at  3000  amperes.  Thus  we  generate  in  every 
.second  a  heat  quantity  of  (Q  =  .24  et),  or  say  30  kilogram 
calories,  in  the  small  space  between  the  electrode  and  the  slag, 
even  though  we  only  assume  40  or  50  volts  as  the  arc  voltage. 
This  amounts  to  over  100,000  calories  given  off  hourly  from  the 
foot  of  the  electrode.  It  follows  that  the  slag  layer  is  the  second 
resistance  between  the  electrode  and  the  metal.  The  heat  thus 
transformed  is  dependent  on  the  thickness  of  the  slag  layer 
and  on  its  constantly  changing  conductivity.  If  we  take  for  this 
an  additional  drop  of  10  volts,  we  add  an  additional  26,000 
calories,  which  is  entirely  independent  of  the  small  amount  of 
heat  appearing  in  the  high  conducting  iron  itself.  The  main  heat 
therefore  manifests  itself  in  the  space  between  the  electrode  and 
the  slag.  The  foot  of  the  electrode  thereby  has  the  gasifying 
temperature  of  carbon.  A  very  considerable  portion  of  the 
heat,  therefore,  enters  the  bath  through  radiation  and  through 
the  carbon  vapor,  having  over  3000°  temperature,  (C.)  which  is 
constantly  thrown  from  the  electrode  onto  the  slag  surface  and 
is  for  the  most  part  greedily  absorbed  by  the  oxygen  in  the  slag." 

From  the  foregoing  general  characteristics  of  the  combined 
arc  and  resistance  furnaces,  as  they  may  be  alluded  to  theoreti- 
cally, it  follows  that  the  heating  of  the  metal  bath  takes  place 
practically  almost  exclusively  through  the  arc  heating  alone,  so 
that  the  above  furnaces  are  fully  entitled  to  be  simply  referred 
to  as  arc  furnaces,  which  is  the  case  in  practice. 

THE  ELECTRODES 

One  of  the  most  important  parts  of  all  arc  furnaces  are  the 
electrodes,  at  the  ends  of  which  the  arc  is  maintained,  and  which 
lead  the  current  to  the  bath. 


ARC  FURNACES  IN  GENERAL  81 

A  most  resistive  to  oxidation  material  is  required  for  electric 
furnace  electrodes  in  any  event,  and  only  carbon  meets  the 
requirements  for  those  coming  directly  in  contact  with  the  bath, 
(if  we  omit  for  the  moment  the  electrodes  of  iron  or  conductors 
of  the  second  class,)  as  of  all  the  metallic  conducting  materials, 
carbon  alone  stands  the  highest  temperatures.  It  is,  of  course, 
to  be  considered  throughout  that  carbon  is  very  liable  to  enter 
into  reactions,  especially  at  the  temperatures  found  in  electric 
furnaces,  so  that  the  metal  bath  must  be  protected  by  a  layer 
of  slag  against  an  undesirable  absorption  of  carbon,  as  is  done 
for  instance  in  the  Heroult,  Girod,  Rennerfelt  and  other  arc 
furnaces  for  steel  making.  If  this  is  done,  carbon  offers  by 
far  the  most  desirable  material  for  arc  furnace  electrodes. 

These  are  made  in  specialty  factories,  or  in  case  of  very  large 
electric  furnace  installations  at  their  own  works.  They  are 
made  by  hydraulic  presses,  being  later  on  carefully  dried  and 
burned.  Here  one  should  strive  to  obtain  a  complete  uni- 
formity of  the  mass,  and  the  greatest  mechanical  solidity. 

Regarding  the  electric  conductivity,  it  is  to  be  noted  that 
this  varies  greatly  when  using  either  carbon  or  the  various  sorts 
of  amorphous  carbon,  charcoal,  coke  or  soot.  We  obtain  a 
higher  conductivity,  the  more  the  finished  electrode  approaches 
the  graphitic  state,  pure  graphite  electrodes  giving  the  very  highest 
conductivity  obtainable.  This  item  is  dwelt  upon  later  in  detail. 

Moving  parallel  with  the  increase  in  the  electrical  conduc- 
tivity is  the  heat  conductivity,  so  that  when  we  have  these 
favorable  electrical  conditions,  i.e.,  when  using  graphite  elec- 
trodes, we  have  the  smallest  Joule  or  fr  losses.  To  be  sure, 
the  largest  thermal  losses  occur  at  the  same  time,  because 
graphite  electrodes,  being  good  conductors,  transmit  large  heat 
quantities  from  the  inner  furnace  to  the  outside. 

We  then  have  before  us  the  interesting  question  concerning 
the  most  advantageous  composition  for  the  electrodes,  i.e., 
finding  out  how  to  gain  their  best  efficiency.  This  question  is 
of  great  importance,  as  the  efficiency  of  the  electrodes  largely 
influences  the  total  efficiency  of  arc  furnaces.  Before  going  in  to  this 
question,  however,  we  will  preface  it  with  a  few  general  remarks. 


82      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Next  to  the  heat  generated  in  the  electrodes,  current  density 
has  the  greatest  influence.  That  is,  the  number  of  amperes  per 
unit  of  electrode  cross-section,  which  of  course  accompanies  the 
electrical  conductivity.  In  accordance  with  a  paper  read  before 
the  "Verein  deutscher  Eisenhiittenleute,"  by  Professor  Borchers, 
in  1908,  an  electrode  material  having  the  conductivity  of  arc- 
lamp  carbons,  commences  to  gasify  its  carbon  when  the  current 
density  is  from  10  to  15  amperes  per  square  millimetre  (6500  to 
9750  amp.  per  square  inch),  whereas  when  the  current  is  from 
.5  to  i.o  amperes  per  sq.  millimetre,  (325  to  650  per  sq.  inch), 
the  temperature  attained  was  from  500  to  600°  C. 

Of  course  these  current  densities  just  mentioned  do  not 
occur  in  electrodes  for  electric  furnaces.  According  to  A.  Helfen- 
stein,  the  electrodes  of  calcium  carbide  furnaces  reach  a  red  heat 
with  only  9  to  10  amperes  per  square  centimetre  (58.0  to  64.5 
amps,  per  sq.  inch).  The  considerably  higher  temperatures  of 
carbon  electrodes  as  used  in  practice  in  arc  furnaces  is  explained 
by  the  electrodes  not  being  heated  by  their  ohmic  resistance 
alone  (f  r  loss),  as  they  are  heated  besides  this  by  the  arc 
temperature  at  the  electrode  end.  The  following  table1,  taken 
from  the  book  by  Wilhelm  Borchers,  "The  Electric  Furnace," 
may  show  the  current  densities  usually  figured  with: 


Electrode  Diam. 

Carbon  Cross-Section 
per  Ampere 

Electrode  Cross-Section 

Load  in  Amperes 
per  Unit 

mm. 

inches 

sq.mm. 

sq.in. 

sq.cm. 

sq.in. 

sq.cm. 

sq.in. 

50 

1.97 

IO 

•0155 

19   63 

3-05 

10. 

65.0 

IOO 

3-93 

12 

.0186 

78.54 

12.12 

8.33 

53-5 

200 

7-97 

20 

.0310 

314.16 

50.0 

5  .00 

32-5 

300 

11.90 

30  to  40 

.0465  to 

706.86 

III  .2 

3-33  to 

21.5  to 

.062 

2-5 

16.0 

400       15  .94 

60  to  90 

.093  to 

1256.64 

200.0 

1.66  to 

10.7 

1 

.14 

I.  II 

7.2 

1The  later  (1916)  type  of  carbon  electrodes  used  in  the  2o-ton  Heroult 
furnace  at  Homestead,  Pa.,  was  24  inches  in  diameter.  As  they  carry  from 
13,000  to  25,000  amperes  per  phase,  the  current  density  is  as  low  as  26  to  46 
amperes  per  sq.  inch  (see  also  page  322),  depending  on  the  voltage  used. 


ARC  FURNACES  IN  GENERAL  83 

It  must  be  seen  from  the  table  that  the  load  per  unit  of  cross- 
section  decreases  as  the  electrode  cross-section  increases,  the 
essential  reason  being  that  the  manufacture  of  electrodes  of  the 
best  quality  becomes  more  difficult  as  their  cross-section  increases. 

It  is  also  evident,  that  it  is  harder  to  make  a  completely  even 
mass  in  a  large  electrode  cross-section,  than  in  a  small  cross- 
section.  It  is  likewise  much  easier  to  obtain  an  even  annealing 
for  thin  electrode  rods,  than  for  thick  rods.  Finally  the  gasifica- 
tion of  p'art  of  the  binding  material  of  electrodes  is  much  more 
uniformly  and  completely  accomplished  in  small  cross-sections, 
than  is  possible  in  large  cross-sections,  in  which  it  is  almost  im- 
possible to  avoid  irregularities.  If  these  facts  illustrate  the 
decrease  of  the  permissible  current  density  with  increasing 
electrode  cross-sections,  and  if  it  appears  that  the  use  of  too  large 
cross-sections  is  not  advisable,  we  find  that  the  considerable 
weight  of  the  carbon  electrodes  is  also  forbidding;  besides  there 
is  irregular  solidity  with  growing  cross-sections. 

Owing  to  this,  it  has  been  found  preferable,  sometimes,  to 
build  up  large  electrodes  of  several  smaller  ones  and  thus  avoid 
one  large  electrode  block.  See  Figs.  6oa  and  606. 

Thus  we  can  use  in  these  smaller  electrodes  the  higher  per- 
missible current  densities,  and  attain  a  smaller  total  electrode 
cross-section,  which  consequently  give  the  much  desired  lower 
thermal  losses.  With  all  this,  we  stand  anew  before  the  question 
of  what  is  the  best  division  between  the  electrical  and  thermal 
losses  in  the  electrodes,  i.e.,  how  shall  their  best  efficiency  be 
attained?  This  theme  has  been  extensively  discussed  in  1909 
and  1911  in  the  Electrochemical  and  Metallurgical  Industry, 
latterly  called  Metallurgical  and  Chemical  Engineering.  The 
principle  articles  are  by  C.  A.  Hansen  and  Carl  Hering.  Even 
though  these  dissertations  could  not  solve  the  question  of  the 
best  electrode  dimensions  completely,  still,  the  results  are  so 
important  that  they  are  presented  here  in  condensed  form. 

As  before  mentioned  •  there  are  two  kinds  of  losses  in  the 
electrodes: 

i.  Losses  through  Joule  heat,  i.e.,  those  in  consequence  of  the 
electric  current  flowing. 


84      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

2.  Losses  through  heat  conduction,  i.e.,  those  occasioned  by 
the  electrode  (being  a  good  heat  conductor)  leading  the  heat 
from  the  inner  furnace  to  the  outside. 

How  complicated  these  conditions  become  by  the  cooperation 
of  these  two  losses  is  evidenced  by  one  of  Hansen's  tests,  for  he 
obtained  the  astounding  result,  when  the  ohmic  resistance  and 
the  current  density  were  increased  to  such  an  extent  that  the 
Joule  losses  doubled — still  the  total  losses  remained  the  same. 

Of  what  importance  the  clearing  up  of  these  conditions  is, 
is  very  evident,  when  we  hear  that  according  to  Hansen  the 
losses  in  a  furnace  operating  with  500  Kw.  can  easily  be  15 
per  cent,  of  the  total  energy  input.  This  would  be  continually 
75  Kw.,  or  with  a  current  cost  of  $4  cent  per  Kw.-hour,  the 
electrode  losses  would  cost  about  56  cents  hourly. 

When  the  electrodes  are  incorrectly  dimensioned,  it  may 
happen  that  thermal  losses  increase  to  such  an  extent,  that  it 
is  no  longer  possible  to  keep  the  whole  bath  molten.  Then  only 
just  that  part  which  is  directly  beneath  the  arc  will  stay  molten, 
while  the  remainder  will  remain  solid,  owing  to  the  heat  transfer- 
ence occasioned  by  the  extravagant  dimensioning  of  the  electrodes. 

These  examples  already  show  that  a  saving  in  the  electrode 
losses  may,  under  certain  circumstances,  be  the  deciding  factor 
for  the  economic  working  of  the  electrode  furnace,  especially  if 
the  price  of  current  be  high,  while  in  other  cases  large  sums  of 
money  could  be  saved,  if  we  succeeded  in  approaching  as 
nearly  as  possible  the  best  theoretical  electrode  dimensions. 

In  order  to  become  acquainted  with  the  conditions  governing 
the  least  losses,  Hansen  made  parallel  tests  with  graphite  and 
carbon  electrodes  which  gave  the  following  results. 

The  efficiency  of  graphite  electrodes  grows  with  increasing 
length  and  increasing  current  densities.  It  is,  however,  im- 
possible to  force  the  current  density  above  certain  limits,  as  the 
electrodes  then  taken  on  temperatures  that  are  too  high,  which 
might  easily  destroy  the  surrounding  brickwork. 

With  ordinary  carbon  electrodes  an  increasing  length  causes 
a  decrease  in  the  efficiency,  whereas  the  Joule  effect  becomes 
much  larger  than  the  thermal  losses. 


ARC  FURNACES  IN  GENERAL  85 

The  experimentally  ascertained  conditions  of  Hansen  are,  of 
course,  only  true  between  certain  limits.  It  is  evident  that  by 
continuing  to  increase  the  length  of  graphite  electrodes,  up  to 
a  certain  point,  a  condition  would  soon  result  where  the 
losses  are  a  minimum.  If  this  point  is  exceeded  then  the  Joule 
effect  would  increase  more  rapidly  than  the  heat  losses  would 
decrease,  and  this  would  result  in  an  increase  of  the  total  losses. 

Similarly  the  minimum  losses  would  be  exceeded  if  the  current 
density  were  increased  beyond  its  best  value. 

These  reflections  led  Hering  to  determine  the  most  favorable 
electrode  dimensions  theoretically.  Though  these  determina- 
tions do  not  always  give  the  greatest  consideration  to  the  con- 
ditions in  actual  practice,  and  the  results  may  only  be  partly 
used  in  practice,  still  they  give  such  interesting  disclosures,  re- 
garding occurring  conditions,  that  they  are  for  this  reason  worthy 
of  note,  and  will  be  given  a  little  later  on. 

Now  next  it  is  evident,  that  under  any  conditions  and  inde- 
pendent of  material,  an  increase  in  the  electrode  cross-section  in- 
creases the  heat  conducting  losses,  simultaneously,  though 
decreasing  the  electrical  losses.  On  the  other  hand  a  lengthening 
of  the  electrode,  namely  on  the  inside  of  the  insulating  brickwork, 
causes  a  decrease  of  the  thermal  and  an  increase  of  the  electrical 
losses.  When  both  cases  are  extreme  the  losses  will  be  infinitely 
great. 

It  is  a  fact,  however,  that  the  Joule  heat  as  well  as  the  heat 
carried  off  through  conduction  are  both  generated  by  electricity. 
Thus  the  object  is  to  bring  the  total  losses  down  to  a  minimum. 

For  this  it  is  quite  necessary  to  know  accurate  values  of  heat 
conductivity  and  specific  resistance  for  every  electrode  material. 
Furthermore,  there  should  be  accurate  results  on  the  indepen- 
dence of  these  values  of  the  temperature.  Fortunately  such 
results  are  now  no  longer  missing.1  To  this  must  be  added 
however,  that  all  electrodes  are  manufactured  articles,  which 
are  not  capable  of  being  prgduced  of  complete  uniformity.  The 
constants  of  these,  (of  proved  material,)  vary  somewhat  with 
the  area  of  the  electrode,  but  for  practical  purposes  the  varia- 

1  See  "The  Proportioning  of  Electrodes  for  Furnaces,"  A.  I.  E.  E.,  April, 
1910,  by  Dr.  Carl  Hering. 


80    ELECTRIC   FURNACES   IN   THE   IRON  AND    STEEL  INDUSTRY 


tions  of  the  constants  at  different  sections  of  the  electrodes 
may  be  disregarded. 

Hering,  in  his  computations,  assumes  what  is  probably  nearly 
or  quite  correct  in  most  cases,  namely,  that  the  heat  gradient 
through  the  wall  is  practically  the  same  as  that  in  the  electrode 
through  the  wall,  and  if  these  two  heat  gradients  are  alike,  the 
assumption  is  correct,  that  is,  he  assumes  that  the  electrode 
is  insulated  throughout  its  entire  length,  so  that  the  heat  is  only 
conducted  away  by  the  end  of  the  electrode,  which  is  on  the  out- 
side of  the  furnace  and  there  usually  cooled  with  water.  He 
further  assumes  that  the  electrode  has  the  exact  same  cross- 
section  throughout  its  entire  length,  and  that  the  change  of 
conductivity  with  temperature  follows  a  straight  line.  However, 
it  may  be  said  that  the  straight  line  temperature  coefficient  is 
not  necessary  for  the  correctness  of  most  formulas,  provided 
the  correct  average  value  is  used,  which  he  calls  the  "electrode 
mean  value"  neither  an  arithmetic  nor  geometric  mean,  but  one 
peculiar  to  electrodes.  There  are,  therefore,  still  some  assump- 
tions which  are  not  borne  out  by  the  facts,  but  are,  however, 
necessary  in  order  to  make  the  conditions  for  theory  and  practice 
more  distinguishable. 

With  the  assumptions  as  made,  Hering  shows  the  conditions 
as  visually  shown  by  Figs.  40  and  41.  In  Fig.  40,  E  E  represents 


7T 


--         E 


FIG.  40. 


-H* 


FIG.  41. 


an  electrode,  which  is  surrounded  about  its  periphery  with  a 
complete  heat  insulator,  so  that  only  the  ends  remain  free,  which 
are  for  instance  kept  cool  by  means  of  water-cooling.  If  we  now 
send  a  comparatively  heavy  current  through  the  electrode,  this 
will  heat  the  latter  strongly  at  the  middle  point  H,  •  until  an 
equalizing  condition  occurs.  As  soon  as  this  is  reached,  the 
entire  Joule  heat  will  be  carried  off  at  the  cooled  electrode  ends, 
while  no  heat  flow  will  occur  at  H. 

If  we  now  cut  the  insulated  electrode  at  H ,  in  order  to  utilize 


ARC  FURNACES  IN  GENERAL  87 

both  parts  as  electrodes  for  an  electric  furnace,  as  it  is  schemati- 
cally shown  by  Fig.  41,  there  will  be  no  change  in  the  situation, 
provided  the  furnace  has  the  same  temperature  which  it  formerly 
had  at  H,  assuming  of  course  that  the  same  current  strength  as 
before  now  flows  through  the  electrodes.  Under  these  con- 
ditions also,  there  will  be  no  heat  loss  from  the  furnace  interior, 
through  the  electrodes  to  the  outside  of  the  furnace. 

The  condition  given  herewith  is  the  ideal  one,  so  that  we 
may  have  only  the  minimum  electrode  losses,  with,  of  course, 
the  previously  made  assumptions. 

Provided  the  assumptions  have  the  limitations  as  originally 
laid  down,  the  losses  will  be  equal  to 

Q  =  Qi  +  —  where  Qi  equals  that  heat  loss,  which  would  be 

carried  from  the  furnace  to  the  outside  by  the  electrode,  if  no 
electric  current  were  flowing,  and  Qz  equals  that  heat  quantity 
which  is  solely  and  alone  generated  by  the  current  overcoming 
the  electrode  resistance  =  i2  r. 

Consequently  Q\  =  c  k  r  -T-;  here  c  =  4.  18,  a  constant,  which 

is  used  for  converting  gram  calories  into  watts. 

k  =  the  electrode  mean  heat  conductivity1  in  gram  calories 

per  second  by  i  cm.  length  and  i  sq.  cm.  cross-section, 

with  the  temperature  difference  appearing  between 

the  hot  and  the  cold  electrode  ends. 
T  =  temperature  difference  between  the  hot  and  cold  electrode 

ends. 
I  =  the  length  of  the  electrode  in  centimetres. 

Furthermore,  Qz  =  iz  r  =  i2  pi  — 

where  r  denotes  the  total  resistance  of  the  electrodes. 

Pi  =  the  mean  electrical  resistivity  per  cubic  centimetre  at 
the  occurring  temperature  difference. 
/  =  length  in  centimetres. 
q  =  cross-section  in  square  centimetres. 


"electrode  mean"  is  that  mean  value  which  is  the  average  value 
tinder  electrode  conditions  as  determined  by  actual  research  by  Hering. 
See  A.  I.  E.  E.,  1910. 


88   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

We  therefore  obtain  the  total  losses,  which  are  carried  away 
from  the  cold  end  of  the  electrode,  as 

_  &  q         i  I 

2  T  I          2   l  Pl  q' 

The  total  energy  losses  carried  off  at  the  cool  electrode  end,  are 
equal  to  the  sum  of  the  heat  losses,  which  would  occur  if  no  current 
flowed  through  the  electrode,  plus  half  of  the  heat  lost  by  means  of 
the  Joule  effect. 

The  losses  are  a  minimum  when  the  pure  heat  losses  are  equal 
to  one-half  those  caused  by  the  Joule  effect,  i.e.,  when 

4. 18  k  T  -r  =  —  i2  pi  — .     In  this  case  the  total  losses  are  equal 
I         2  q 

to  the  Joule  heat  losses  or  i2  r,  and  hence  no  heat  would  be  car- 
ried from  the  furnace  by  conduction.  From  the  equation  for 
the  minimum  losses, 

4. 1 8  k  T  -J-  =  —  i2  pi  — ,  it  follows  that 

_i  =     i  rp7 

If  this  result  is  then  substituted  for  y  in  the  general  equation 
for  the  total  losses,  we  have: 

Q  =  4. 18  k  T  —r  H i2  pi  — .     In  order  to  attain  the  minimum 

losses  we  have  the  requirement 

Qmin  =  2.892  V  k  T  pi.  The  equation  for  Qmin  shows  that  the 
minimum  losses  are  determined  by  the  material  constants  k 
and  pi,  the  temperature  differences  between  the  hot  and  cold 
electrode  ends,  and  the  current  strength.  It  is  independent 
of  the  absolute  dimensions  of  the  electrodes,  for  of  these  it  is 
only  required  to  maintain  a  definite  relation  between  the  cross- 
section  and  the  length  in  accordance  with  the  equation  for  -;-• 

If  we  substitute  in  the  equation  for  Qmin  the  specific  electrical 
conductivity  per  cubic  centimetre,  x  =  — ,  in  place  of  the  specific 


ARC  FURNACES  IN  GENERAL  89 

resistance,  we  obtain 

This  equation  shows  that  the  least  losses  are  fixed  for  a  certain 
definite  temperature  on  account  of  the  relation  between  the  heat 
conductivity  and  the  electrical  conductivity.  In  accordance 
with  this,  the  best  material  for  the  electrodes  is  that  which  has  the 
lowest  ratio  of  the  heat  conductivity  to  the  electrical  conductivity. 

From  the  equation  for  the  minimum  losses,  it  follows  that  an 
increase  of  the  temperature  difference  between  the  hot  and 
cold  electrode  ends  only  influences  the  losses  in  proportion  to  the 
square  root  of  these  differences. 

If  we  again  consider  the  equation, 

—r  =  .  345  i  -J  7^-  we  see,  that  with  a  given  material,  a  given 

current  strength,  and  a  given  temperature  difference,  the  elec- 
trode losses  would  remain  the  same  for  entirely  different  cross- 
sections,  provided  the  proportion  between  the  cross-section  and 
the  length  remained  unchanged. 

From  this  we  now  learn:  //  it  be  desired  to  save  on  electrode 
material  when  having  a  minimum  of  losses,  then  the  electrode  is  to 
be  made  as  short  as  possible.  Generally  the  electrode  length  is 
primarily  determined  by  the  practical  demands  of  the  furnace 
operation,  so  that  a  certain  minimum  distance  of  electrode 
length  cannot  be  exceeded.  The  length  of  electrode,  therefore, 
having  been  determined,  the  cross-section  can  be  calculated  by 

using  the  formula  -y. 

It  is  well  to  mention  here  that  it  can  be  assumed  that  all  these 
calculations  only  retain  their  full  correctness,  provided  the 
electrodes  are  protected  by  insulation  throughout  their  whole 
length.  It  may  be  repeated  though  that  the  heat  gradient 
through  the  wall  is  practically  the  same  as  that  in  the  electrode 
through  the  wall,  and,  if  so,  the  assumptions  are  correct.  If  these 
two  heat  gradients  differ  materially,  then  an  increase  of  the  cross- 
section,  in  the  same  proportion  to  the  length,  causes  a  decided 
increase  in  the  electrode  surface  and  with  it  naturallv  an  in- 
crease of  the  heat  losses. 


90    ELECTRIC   FURNACES   IN   THE   IRON   AND    STEEL   INDUSTRY 

From  the  derived  formulas,  it  is  evident  that  the  current 
strength  influences  the  size  of  the  losses.  Consequently,  it  would 
be  requisite  to  have  the  smallest  possible  current  at  high  voltages. 
Unfortunately,  this  demand  cannot  be  fulfilled,  without  leaving 
the  total  efficiency  of  the  furnace  out  of  consideration,  for  it  is 
always  well  to  keep  in  mind  that  the  electrode  losses  considerably 
affect  the  furnace  efficiency,  but  are  not  the  sole  factors  that 
carry  weight  with  it.  This  point  is  discussed  further  bn. 

In  place  of  the  current  strength  in  the  formula 

Pi 


we  can  insert  the  current  density  A  =  —  ,  and  obtain 


This  formula  produces  a  combination  showing  the  best  con- 
ditions between  cross-section  and  length  together  with  a  current 
density  fit  for  use.  This  seems  advantageous,  because  by  over- 
stepping the  permissible  current  density  limits,  it  is  very  easy 
to  endanger  the  furnace  operation.  On  page  84  mention  has 
been  made  of  these  tests  by  Hansen.  However,  this  formula 
also  has  the  disadvantage,  that  it  determines  the  electrode  length 
arithmetically,  which  is  not  fully  determinable  for  practical 
reasons.  And  the  value  of  this  derived  formula,  practically  only 
consists  in  bringing  forth  a  clear  idea  of  the  conditions  of  an 
ideal  case.  This,  however,  does  not  infer  that  the  above  formula 
is  the  ideal  case  and  is  not  considered  so  by  Hering.  It  should 
be  the  ambition  of  every  furnace  designer  to  come  as  near  to 
this  as  possible. 

In  order  to  be  able  to  utilize  these  rules  and  references,  it 
is  necessary  to  have  useful  constants  for  the  different  con- 
ductivities of  different  electrode  materials.  Fortunately  there 
is  now  no  lack  of  these  at  present.1  Even  though  only  a  few 
values  are  given  hereafter,  it  must  be  observed  that  they  have 
reference  to  a  certain  definite  material,  which  just  happened 

1  See  A.  I.  E.  E.,  April,  1910. 


ARC  FURNACES  IN  GENERAL  91 

to  be  used  for  these  determinations,  and  that  products  from 
other  factories  would  give  results  deviating  from  these,  more  or 
less.  Nevertheless,  the  figures  comparing  the  graphite  and 
carbon  electrodes  may  be  regarded  as  typical,  and  can  conse- 
quently be  used  in  practise  for  electrode  designs. 

Hansen  gives  the  following  figures  for  temperature  differences 
up  to  3000°  Centigrade: 

Material.  Pi  k 

Graphite1  ...............................  000812     .16 

Carbon2  ................................  00183       -Ol6 

The  proportion  between  the  electrical  resistance  of  carbon  and 
graphite  is  as  2.25  :  i,  whereas  the  heat  conductivity  of  graphite 
is  ten  times  as  great  as  that  of  carbon. 

Relative  to  the  current  densities  Hansen  believes  it  safe  to 
figure  with  the  following  values:3  For  graphite,  150  amps,  per 
square  inch.  This  equals  4.3  sq.  mm.  per  amp.  or  23.25  amp. 
per  sq.  cm.  For  carbon,  50  amp.  per  square  inch.  This  equals 
13  sq.  mm.  per  amp.,  or  7.75  amp.  per  sq.  cm.  Substituting  these 

values  in  the  ratio  -|-  in  accordance  with  the  equation: 


for  instance  for  20000  amp.,  and  3000°  C,  we  have  for  graphite, 


q  |     .000812 

j  =  -345  X 20000^  .I6X3000  -  9-0 


and  for  carbon, 


q  I       .00183 


=  -345  X  20000      ^^^-  —  =  4*57 
i.e.,  for  equal  electrode  lengths  (which  would  be  required  for  the 
same  furnace)  of  graphite  as  well  as  for  carbon,  a  carbon  electrode 

would  have  to  have  —  -  —  =  4-73  times  the  cross-section  of  a  graph- 
ite electrode. 

1  Specific  resistance  ohms  per  inch  cube  =  .000320. 

2  Specific  resistance  ohms  per  inch  cube  =  .000721. 

Compare  the  values  dependent  on  the  cross-section  as  given  on  page  82. 
See  also  page  81. 


92      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

After  the  relation  for  ~  is  given,  we  can  either  assume  the 

required  electrode  length  as  given  (on  account  of  the  practical 
furnace  requirements),  and  thereafter  determine  the  cross- 
section,  which  could  then  be  regulated  by  permissible  current 
densities.  We  could,  however,  also  figure  from  a  given  current 
density  as  a  basis,  and  from  the  cross-section  thus  determined, 
calculate  the  electrode  length,  which  would  then  have  to  have  its 
practical  applicability  proved. 

Should  we  choose  the  latter  method,  we  may  calculate  the 
cross-section  based  on  a  certain  current  density  deemed  per- 
missible, and  based  on  Hansen's  values,  for  instance,  for  the 
electrode  cross-sections  of  this  material.  The  example  cited 
was  for  20,000  amperes.  We  then  have: 

2OOOO 

graphite  =  —     —  =  860  sq.  cm. 
23-25 

,        20000  .  N 

(  =  -—  =  133  sq.  inches) 

on  account  of  the  proportion,  therefore,  of  y  =  9,  we  obtain  a 

length  of  95  cm.,  or  37.4  inches. 

If  we  assume  that  this  length  is  satisfactory  to  the  furnace 
operation,  then  this  same  length  will,  of  course,  have  to  be  kept 
for  the  carbon  electrode,  and  in  case  a  minimum  of  losses  is  also 
desired  here,  we  would  have  for  the  carbon  electrode  cross- 
section  (based  on  the  calculated  relation  of  -y  =  42.57) 

g  carbon  =  4044  sq.  cm. 

(=  1591  sq.  inches). 

From  this,  with  20000  amps.,  we  have  a  current  density  of 
20000 


4044 


4.9  amp.  per  sq.  cm. 


,        20000  .      , 

(=   -     —  12.5  amp.  per  sq.  m.), 

which  would  show  that' according  to  the  values  given  on  page  82, 
these  are  sufficiently  high,  so  that  an  enlargement  of  the  cross- 
section  would  recommend  itself,  and  perhaps  a  simultaneous 


ARC  FURNACES  IN  GENERAL 


93 


increase  in  the  electrode  length,  in  order  to  stay  as  close  as 
possible  to  the  minimum  losses. 

Besides  this  it  is  interesting  to  become  acquainted  with  the 
losses  as  they  appear  in  the  given  example,  either  when  using 
graphite  or  carbon  for  the  electrodes.  The  equation  for  the 
minimum  losses  was: 

Qmin  =  2.89  *V*7^ 

By  substituting  the  values  for  graphite,  we  obtain  Qmfn  =  36 
KW  and  for  carbon  Qmin=  17  KW.,  i.e.,  assuming  that  the  given 
constants  are  correct,  the  losses  for  graphite  would  be  about 
twice  as  large  as  those  for  carbon. 

This  condition,  however,  only  holds  good,  when  the  electrodes 
are  heat  insulated  for  their  entire  length  as  previously  mentioned. 

In  accordance  with  the  values  heretofore  cited  on  page  82, 
for  the  usual  current  density  values  for  electric  arc  furnace 
carbon  electrodes,  it  seems  that  the  figure  of  7.75  amps,  per 
square  centimetre  (50  amps,  per  square  inch),  which  Hansen 
gives,  is  extraordinarily  high.  It  is  therefore  not  advisable  to 
use  these  figures,  which  gives  much  too  short  electrodes  for 
practical  furnace  constructions,  as  the  example  showed.  It  is 
better  to  use  those  values  given  on  page  82,  which  simultaneously 
take  into  consideration  the  influence  of  the  electrode  cross- 
section  enlargement. 

The  figures  given  in  the  following  tables  are  from  tests  made 
by  Hansen  and  published  by  him.  On  the  one  hand  for  graphite 
electrodes  made  by  the  International  Acheson  Graphite  Co., 
and  on  the  other  for  carbon  electrodes  made  by  the  National 
Carbon  Co.;  these  may  show  the  influence  of  the  cross-section 
enlargement  on  the  material  constants  even  a  little  better. 
ACHESON  GRAPHITE  ELECTRODES 


Diameter  or 
Cross-Section 

pi  =  Resistance 
ohms  per  cm.  cube 

Diameter  or 
Cross-Section 

pt  =  Resistance 
ohms  per  in.  cube 

5.08  cm.  diam. 
7.62  cm.  diam. 
io.i6xio.i6sq.cm. 
15.24x15.24  sq.cm. 

.00092  to  .00093 
.OOI03tO  .00109 

.0009610  .00101 
.  00084  to  .  00085 

2  inches  diam. 
3  inches  diam. 
4  in.  x  4  in. 
6  in.  x6in. 

.  000362  to  .  000366 
.000406tO  .000429 
.000378  to  .000397 
.000331  to  .000335 

94      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

These  measurements  were  made  at  a  temperature  of  25°  C. 
With  increasing  temperature  the  resistance  of  graphite  falls 
as  is  well  known.  According  to  Hansen,  this  is  as  follows: 

At       25°  Centigrade 100% 

94% 

81.5% 

"         66% 

"         65% 

"        68% 

.-     69% 

For  carbon  electrodes  Hansen  found  the  following  values  de- 
pending on  the  cross-section: 

NATIONAL   CARBON   COMPANY   ELECTRODES 


400" 
8ooc 

1200° 
I600° 
2000° 
2200° 


Size  of 
Cross-Section 

pi  =  Resistance 
in  ohms  per  ccm.  cube 

Size  of 
Cross-Section 

Pz  =  Resistance 
in  ohms  per  inch  cube 

10.16x10.  i6sq.cm. 
15.24x15.24  sq.cm. 
20.23x20.23  sq.cm. 
45.72x45.72  sq.cm. 

•00457 
.00856 
.00594  to  -OO7I 
.014      to  .0254 

4  in.  x   4  in. 
6  in.  x    6  in. 
8  in.  x    8  in. 
18  in.  x  18  in. 

.OOlSo 
.00337 
.00234  to  .00279 
.00551  to  .0100 

Referring  to  the  last  of  these  values,  it  is  well  to  note  that  this 
test  was  made  on  an  electrode  delivered  4  years  ago,  and  it  is 
possible  that  better  results  have  been  attained  since  then,  for 
large  electrodes.1 

Hansen  also  made  some  investigations  with  carbon  electrodes 
in  order  to  determine  the  influence  of  temperature.  He  found 
that,  with  an  increasing  temperature,  the  carbon  continually 
proceeded  to  graphitize,  so  that  after  the  electrodes  had  cooled 
down,  the  original  figures  for  the  specific  resistance  no  longer 
held  true,  but  were,  instead,  much  better. 

The  following  table  shows  how  the  specific  resistance  of  the 
cold  carbon  electrode  falls,  in  case  the  electrode  has  been  pre- 
viously heated  to  the  temperature  shown  in  the  table: 


1  In  1916  the  National   Carbon  Co.  state  that  their  "Steel  furnace  elec- 
trodes have  a  resistance  of  about  .0025  to  .0030  ohms  per  inch  cube." 


ARC  FURNACES  IN  GENERAL  95 

Resistance  in  the  cold  condition 100% 

After  heating  up  to  1200°  C 91 .6% 

"  "      1600°  C 87.% 

«  «  a  o  /~>  ffrf 

2000°  C 77-6% 

((  ((  ((  o  /~i  x-         rrf 

2400°  C 65.9% 

"  «  «        •  o       o  /-I  /7y 

2800°  C 5°-9% 

«  «  «  o   r<  Crf 

3SOO    C 22.4% 

Here  the  last  figure  approaches  that  which  would  be  obtained 
with  graphite  electrodes  under  the  same  conditions. 

Besides,  Hansen  gives  as  an  average  figure  of  many  tests  made 
with  commercial  carbon  electrodes  when  heated  to  1200°  C.,  a 
resistance  value  equal  to  60  per  cent,  of  that  measured  in  the 
cold  state. 

After  the  electrodes  have  once  been  in  operation,  the  uni- 
formity of  the  material  constants  disappear  in  all  parts  of  the 
cross-section  or  the  length,  owing  to  the  uneven  heating  of  the 
carbon  throughout  its  entire  length.  On  this  account  Hansen 
takes  the  practical  resistance  at  1200°  C.,  at  only  40  per  cent,  of 
its  cold  figure. 

As  for  the  rest,  we  again  point  to  the  figures  which  were  used 
in  the  arithmetical  example  on  page  76. 

The  remarks  regarding  the  best  dimensioning  of  the  electrodes, 
have  a  certain  practical  significance,  and  that  is  why  they  have 
been  discussed  here.  It  is  well  to  be  warned,  though,  that  too 
great  stress  be  not  placed  on  these  theoretical  opinions. 

It  is  to  be  noted  that  the  derived  formulae  are  only  strictly 
accurate  for  such  cases,  where  the  electrode  is  protected  from 
heat  losses  between  its  hot  and  cold  ends-  and  that  this  case 
never  appears  in  practise.  It  is  further  to  be  observed,  that  the 
operation  of  our  arc  furnaces  necessitates  a  shortening  of  the  elec- 
trodes, and  consequently  considerable  electrode  lengths  appear, 
which  are  not  taken  into  consideration  in  the  formula,  because 
they  lie  outside  of  the  water  cooling.  Furthermore,  the  formula 
are  not  the  only  measure  for  the  losses  which  actually  appear  in 
arc  furnaces,  irrespective  of  the  restrictions  just  made.  Besides 
the  pure  radiating  losses,  there  are  for  instance  the  contact  losses, 
where  the  current  carrying  copper  conductor  clamps  onto  the 


96      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

electrode.  And  above  all  it  is  a  noticeable  fact,  that  on  the  one 
hand,  the  size  of  the  cross-section  is  of  the  greatest  influence  on 
the  efficiency  of  the  furnace,  while  on  the  other  we  see  that  the 
electrode  length  is  primarily  settled  by  practical  considerations 
accompanying  the  furnace  operation. 

We  see,  therefore,  that  just  this  relation  between  cross- 
section  and  length  of  electrode,  which  is  of  striking  importance 
in  accordance  with  the  formula  for  the  minimum  losses,  cannot  be 
freely  determined  according  to  the  arithmetical  values.  After 
all,  the  benefit  of  the  calculation  for  the  minimum  losses  lies  in 
the  fact  that  it  allows  us  to  ascertain  the  heat  dimensions  which 
lie  between  the  given  limits  of  practical  requirements,  that  we 
may  come  as  near  them  as  possible. 

Turning  again  toward  the  practical  side  of  the  electrode 
question,  we  find  an  interesting  work  of  Hansen's,  which  deals 
with  the  burning  away  of  the  electrode  or  electrode  consumption. 

This  question  is,  of  course,  of  equal  importance,  as  the  striv- 
ing after  the  least  electrical  losses,  or  a  high  efficiency;  for  this 
point  is  of  considerable  influence  on  the  operating  costs. 

The  consumption  of  electrodes  may  occur: 

1.  In  the  worst  case  when  the  electrode  breaks; 

2.  By  the  arc  formation  which  causes  a  gasifying  of  the  carbon 
and 

3.  By  oxidation. 

Those  under  the  first  heading,  which  are  by  far  the  most 
unpleasant,  seldom  or  never  occur  today,  as  long  as  the  cross- 
section  and  lengths  used  are  not  too  large.  Too  large  cross- 
sections  are  always  to  be  avoided,  so  that  if  high  currents  cannot 
be  avoided,  it  is  better  to  use  graphite  in  place  of  carbon  elec- 
trodes. Furthermore,  it  is  to  be  observed  that  a  new  electrode 
must  not  be  placed  in  the  hot  furnace  in  its  cold  state,  as  small 
particles  are  easily  liable  to  crack  off,  on  account  of  the  great 
prevailing  temperature  differences.  It  is  therefore  commendable 
to  heat  the  electrodes  slightly  before  placing  them  in  use. 

The  losses  under  the  second  heading  are  self-evident  and 
unavoidable,  so  that  nothing  remains  to  be  said  about  them. 


ARC  FURNACES  IN  GENERAL  97 

On  the  contrary  a  much  greater  interest  manifests  itself  in 
the  electrode  consumption  on  account  of  the  oxidation. 

Moissan  found  that  amorphous  carbon  commences  to  oxidize 
at  as  low  a  temperature  as  375  to  490°  C.,  whereas  graphite  first 
begins  to  oxidize  at  temperatures  of  665  to  690°  C.  These  values 
though  were  observed  with  powdered  material  and  not  with  solid 
rods.1  Finally,  Collins,  FitzGerald,  and  Johnson  maintain  that 
graphite  possesses  a  greater  resistivity  against  oxidation  than 
carbon  does 

Contrary  to  this, '  Hansen  observed  that  the  losses  with 
graphite  electrodes  are  greater  than  those  with  carbon  electrodes. 
In  making  these  tests,  graphite  rods  of  the  Acheson  Graphite  Co., 
and  carbon  rods  of  the  National  Carbon  Co.  were  used.  The 
reason  for  the  higher  consumption,  when  using  graphite  rods, 
as  given  by  Hansen,  is  that  at  temperatures  of  1300  to  1400°  C., 
the  graphite  particles  cracking  off  are  so  large,  that  some  of 
them  could  be  picked  up  unconsumed.  This  phenomenon 
disappeared  when  the  heating  occurred  in  carbonic  acid 
gas,  which  proves  that  the  cracking  off  of  the  electrode 
particles,  when  using  graphite,  leads  us  back  to  the  oxidizing 
influence. 

This  investigation  shows  that  it  is  impossible  to  accurately 
determine  in  advance  just  what  the  electrode  consumption  will 
be.  For  this  is  so  dependent  on  all  oxidizing  influences,  that 
even  the  tight  or  less  tight  closing  of  the  working  doors,  or  the 
piercing  of  the  electrodes  through  the  furnace  roof,  or  the  working 
in  a  more  or  less  reducing  atmosphere,  may  cause  considerable 
changes  in  the  electrode  consumption. 

Oxidizing  losses  not  only  affect  the  electrode  consumption, 
but  the  power  consumption  of  the  furnace  as  well,  i.e.,  the 
efficiency.  This  is  evident  from  the  following  tests. 

Hansen  operated  a  small  Heroult  furnace  of  150  kg.  (330 
Ibs.)  capacity,  with  graphite  electrodes  of  io.i6x  10.16  sq.  cm. 
(16  sq.  inches)  cross-section  and  106.  cm.  (40  inches)  long. 

1  These  values,  however,  seem  quite  reliable  since  we  find  data  published 
from  electrode  manufacturers  which  give  the  temperature  of  oxidation  in  air 
at  640°  C.,  and  500°  C.,  respectively,  for  graphite  and  carbon. 


98      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

With  this  arrangement  he  succeeded  in  melting  a  150  kg.  charge 
with  150  kw.-hrs. 

Later  on  a  similar  furnace  was  operated,  but  for  300  kg. 
(660  Ibs.),  having  the  same  electrodes.  It  was  established  here 
through  various  tests,  that  the  power  consumption  of  the  larger 
furnace  had  the  ratio  of  1.2  to  i  compared  to  the  smaller  furnace, 
even  though  a  larger  furnace  usually  has  comparatively  smaller 
thermal  losses  than  a  smaller  furnace.  After  graphite  electrodes 
of  15.24  x  15.24  cm.  sq.  (36  sq.  inches),  and  101.6  cm.  (40  inches), 
long  were  used,  the  larger  furnace  gave  a  somewhat  better  power 
consumption  than  the  smaller  one. 

The  tests  further  showed  that-  the  power  consumption  rose, 
as  soon  as  the  electrode  (the  end  toward  the  molten  metal)  be- 
came more  and  more  pointed  under  the  oxidizing  influences. 
The  difference  in  power  consumption  when  working  with  the 
full  cross-section  compared  to  the  operation  with  a  pointed  one 
was  as  much  as  30  per  cent. 

This  test,  as  well  as  others  made  with  various  electrode  cross- 
sections  in  the  300  Kg.  (660  Ib.)  trial  furnace,  show  that  a  larger 
cross-section  causes  a  decrease  in  the  losses.  This  may  be 
primarily  caused  by  the  fact  that  a  larger  cross-section  permits 
a  more  favorable  dissemination  of  energy  throughout  the  whole 
charge,  and  furthermore,  because  the  full  and  larger  electrode 
cross-section  acts  as  an  umbrella,  which  considerably  lessens 
the  heat  radiation  toward  the  furnace  roof.  The  umbrella 
action  of  the  electrode  also  has  the  additional  advantage  of 
keeping  the  roof  from  deteriorating  too  rapidly.  This,  however, 
changes  as  soon  as  the  electrode  takes  on  its  pointed  form. 

Hansen  established  that  a  more  or  less  strong  sharpening  to  a 
point  of  the  electrode  occurs  in  all  arc  furnaces,  under  the  oxidizing 
influence  which  takes  place  during  the  working  period.  The  trials 
carried  out  to  protect  the  electrodes  by  suitable  coverings  of  car- 
borundum, water-glass,  etc.,  against  the  oxidation,  have  not  been 
successful,  for  it  has  not  been  possible  to  make  the  covering 
durable  with  the  prevalent  temperature  differences,  occurring 
during  the  furnace  operation.  We,  therefore,  have  to  figure  with 
a  certain  burning  away  of  all  electrodes,  owing  to  the  oxidation. 


ARC  FURNACES  IN  GENERAL  99 

Aside  from  the  three  reasons,  which  have  so  far  been  given 
to  determine  the  electrode  consumption,  there  must  still  be 
mentioned  the  additional  loss  caused  by  the  stub  ends.  The 
length  of  this  stub  end  depends  largely  on  the  distance  between 
the  molten  metal  and  the  furnace  roof.  Recently  newer  methods 
have  been  devised  which  now  render  it  possible  to  attach  the 
electrode  remainders  to  the  new  electrodes,  thus  assuring  a  most 
complete  use  of  the  electrode  material.  This  is  gone  into  further 
in  the  chapter  on  the  Heroult  furnace. 

During  the  discussion  of  the  electrode  conditions,  we  have 
often  compared  the  graphite  with  the  carbon  electrodes.  Is 
therefore  one  recommended  above  the  other?  To  this  question 
this  reply  may  be  given:  Graphite  electrodes  mainly  have  the 
advantage  of  greater  resistivity,  and  greater  mechanical  firmness. 
This  advantage,  though,  must  be  purchased  at  a  far  higher 
price,  compared  to  carbon  electrodes.  Large  electrode  surfaces 
tend  to  save  energy,  and  consequently  it  is  better  to  work  with 
low  current  densities.  For  the  graphite  electrode  loses  its  im- 
portance, i.  e.,  its  high  electrical  conductivity,  whereas  its 
disadvantage  of  a  high  heat  conductivity  falls  heavily  in  the 
balance,  so  that  the  graphite  electrode  always  has  a  lesser 
efficiency  than  the  carbon  electrode  (see  page  94). 

From  all  this  it  is  apparent,  that  one  would  at  first  endeavor 
to  utilize  carbon  electrodes,  at  least  as  long  as  these  can  still 
be  made  of  good  quality  and  at  the  desired  cross- sections.  It 
is  only  with  the  largest  furnaces,  where  the  cross- sections  would 
become  so  large,  that  uncertainties  would  enter  the  operation, 
through  breakages,  for  instance,  that  one  would  be  willing  to 
pocket  the  disadvantages  of  the  graphite  electrode,  in  order  to 
gain  the  important  advantage  of  definite  and  sure  operating 
conditions. 

THE   ELECTRODE   COOLING 

Previously  when  discussing  electrode  conditions  it  was 
always  assumed  some  water  cooling  would  be  arranged  at  the 
place  where  the  electrode  leaves  the  furnace  roof,  by  means  of 
which  it  would  be  possible,  to  lower  the  temperature  of  the 


100     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

electrode  as  much  as  100  or  200°  C.  It  was  also  shown  that  the 
electrode  material  may  occasion  considerable  losses  on  account 
of  the  oxidation,  and  this  gives  us  the  first  reason  which  forces 
the  application  of  electrode  cooling  upon  us. 

If  insufficient  cooling  was  provided,  so  that  the  electrode, 
where  it  issues  from  the  furnace,  is  not  cooled  below  the  tem- 
perature, where  the  oxidation  begins,  then  the  unavoidable 
oxidation  in  the  circulating  atmosphere  would  considerably 
reduce  the  cross-section.  This  would  be  followed  by  an  increase 
in  the  electrical  resistance,  hence  a  stronger  heating  up  of  the 
cross-section  already  weakened,  and  therefore  an  increasing 
temperature  with  increasing  consumption,  so  that  in  the  shortest 
space  of  time  a  change  of  electrodes  would  be  required. 

If  an  intensive  water  cooling  is  already  unavoidable,  this 
will  simultaneously  act  protectingly  on  the  uniformity  of  the 
furnace  operation.  Thus  the  contact  arrangements  which 
connect  the  copper  conductors  to  the  carbon  electrodes  are  kept 
from  being  destroyed.  Supposing  we  assume  that  the  electrode, 
even  outside  the  furnace,  has  a  comparatively  high  temperature 
as  well,  then  there  would  be  such  an  increase  in  the  heating  of 
the  contact  pieces,  that  their  hold  on  the  electrodes  would  be 
loosened,  and  with  other  designs  they  would  burst,  so  that  in 
both  cases  the  furnace  operation  would  fail,  on  account  of  a 
break  in  the  electrode  contacts,  quite  irrespective  of  any  damage 
done  by  the  flames  shooting  through  the  roof,  where  the  elec- 
trodes enter. 

The  water-cooling  device  is  also  responsible  for  the  long  life 
to-day  of  the  arc  furnace  contact  clamps.  At  the  same  time,  it 
fulfils  a  third  and  very  important  purpose.  It  was  shown  in 
Chapter  II  that  all  refractory  materials  used  in  electric  furnace 
construction  are  conductors  of  the  second  class,  and  as  such 
obtain  higher  conductivities  with  increasing  temperatures.  This 
also  holds  for  the  brickwork  between  which  the  electrodes  of  arc 
furnaces  lie.  It  is  apparent  that  these  roof  bricks  become  more 
and  more  conducting  with  increasing  temperatures,  whereas  they 
can  be  regarded  practically  as  non-conductors  with  low  or  even 
moderate  temperatures.  In  order  to  avoid  a  strong  oxidation 


ARC  FURNACES  IN  GENERAL  101 

of  the  electrodes,  and  to  attain  the  best  possible  thermal  effi- 
ciency, it  is  necessary  to  have  the  closest  fit  where  the  electrodes 
protrude  through  the  furnace  roof.  Thus,  it  is  immediately 
apparent,  that  when  the  roof  refractories  are  little  resistant,  i.e., 
when  their  temperature  is  high,  then  the  small  spaces  between 
the  electrodes  and  the  surrounding  roof  bricks  are  easily  bridged 
over  with  tiny  arcs,  which  in  turn  cause  currents  to  flow  through 
the  refractory  material  from  one  electrode  to  the  other. 

The  current  flowing  through  the  brickwork  will  be  higher, 
as  the  voltage  increases  between  the  different  electrodes,  as  the 
distance  between  the  electrodes  becomes  less  and  the  temperature 
of  the  brickwork  between  the  electrodes  rises.  That  these 
currents  flowing  through  the  refractory  material  may  be  of  great 
importance  is  shown  in  an  article  by  Coussergues  after  seeing  a 
Stassano  furnace.  In  a  one-ton  furnace,  when  the  arc  was 
interrupted  and  the  voltage  was  120,  there  was  still  a  current  of 
300  amperes  flowing  through  the  brickwork  from  electrode  to 
electrode.  It  is  to  be  noted  here,  that  the  entrance  of  the 
electrodes  to  the  furnace  is  provided  with  water-cooling  contri- 
vances. If  an  attempt  were  made  in  such  a  case  as  this,  to  do 
away  with  the  water-cooling,  then  the  temperature  of  the  brick- 
work in  the  neighborhood  of  the  electrodes  would  rise  consider- 
ably, the  resistance  between  electrode  and  electrode  would 
thereby  further  decrease,  and  still  stronger  currents  would 
traverse  the  brickwork.  The  result  would  be  a  considerable 
increase  in  the  energy  consumption,  while  a  strong  heating 
ensues  at  the  wrong  place,  and  at  the  same  time  there  would 
be  a  quick  destruction  of  the  very  highly  heated  roof  due  to  the 
current  flowing. 

In  accordance  with  the  foregoing,  it  is  established  that  the 
utilization  of  water  cooling  with  arc  furnaces  offers  important 
operating  advantages,  even  though  there  is,  of  course,  a  certain 
heat  loss  on  that  account,  which  is  unavoidable  up  to  certain 
limits.  Aside  from  this  there  is  still,  under  some  circumstances, 
a  small  electrical  loss,  which  may  appear  when  currents  from  the 
electrode  find  their  way  to  the  cooling  chambers,  and  are  thence 
grounded  by  the  water. 


102     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 
THE  ELECTRODE  REGULATION 

In  discussing  the  arc  it  was  shown  that  it  can  only  be  main- 
tained, provided  a  certain  distance  between  the  electrode  and 
the  bath,  or  from  electrode  to  electrode  in  radiating  arc  furnaces, 
is  not  exceeded,  as  otherwise  the  arc  will  be  interrupted.  It  is 


FIG.  410. 

therefore  necessary  to  watch  the  length  of  the  arc.  This  is  easily 
accomplished  with  the  aid  of  a  voltmeter  or  an  ammeter.  The 
electrodes  are  then  regulated  in  accordance  with  readings  of  the 
controlling  instruments. 

Even  though  a  manually  operated  regulation  of  the  electrodes 


ARC  FURNACES  IN  GENERAL  103 

is  possible,  as,  for  instance,  with  the  Stassano  or  Rennerfelt 
furnace,  we  find  the  equipment  with  automatic  regulation,  as 
used  in  the  arc  furnaces  of  Heroult  and  Girod  to-day,  has 
several  advantages. 

In  both  cases,  i.e.,  either  hand  or  automatic  regulation,  this 
is  accomplished  with  the  aid  of  gears,  which  are  often  driven 
by  an  electric-motor  in  order  to  handle  them  faster  and  more 
accurately.  In  accordance  with  the  indications  on  the  measuring 
instruments,  the  motor  is  started  either  to  the  right  or  left  by 
throwing  a  double-throw  switch,  which  either  raises  or  lowers 
the  electrode. 

The  General  Electric  electrode  regulator  (see  Fig.  410),  in- 
vented by  Seede,  has  especial  advantages  from  the  standpoint 
of  simplicity,  reliability,  and  low  repair  costs.  There  are  no 
moving  parts  to  get  out  of  order,  and  the  few  replacements  are 
taken  from  standard  equipment,  few  in  number,  and  can  be 
quickly  replaced.  The  regulation  given  by  this  device  is  as  good 
as  can  be  had,  many  hundreds  of  these  regulators  giving  evi- 
dence of  this  service.  It  is  so  arranged  that  besides  automatic 
regulation  there  is  also  push-button  control  of  the  motors,  and 
independent  hand  regulation.  When  automatically  operated, 
the  speed  is  low,  whereas  when  hand  regulation  is  resorted  to 
the  speed  is  high.  Both  of  these,  however,  are  variable.  The 
furnace  kilowatt  input  may  also  be  quickly  varied.  There 
are  suitable  relays  to  prevent  saturating  the  bath  with  carbon 
in  case  the  electrode  circuits  are  opened.  Fig.  416  shows  the 
electrical  connections. 

The  Thury  regulator,  invented  in  1898,  is  also  used  for  this 
automatic  regulation.  It  is  made  by  Ateliers  H.  Cuenod,  A.G., 
at  Chatelaine  near  Geneva,  Switzerland,  and  in  the  United 
States  by  the  Westinghouse  Electric  and  Manufacturing  Co., 
Pittsburg,  Pa. 

The  principal  part  of  a  Thury  regulator  is  an  electro-magnetic 
scale,  which  is  balanced  when  the  current  and  voltage  condi- 
tions are  normal.  When  deviations  occur  in  the  normal  circuit 
conditions,  they  throw  the  lever  out  of  balance.  These  scales 
are  used  then  to  throw  a  switch  to  either  one  side  or  the  other, 


104   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


so  that  the  current  for  the  driving  motor  enters  it  either  from 
one  or  the  other  side,  thus  bringing  about  the  corresponding 
motion  of  the  electrode. 

The  switching  mechanism  of  the  old  Thury  regulator  consists 
of  a  small  constantly  running  auxiliary  motor,  which  moves  a 


Is  not  furnished  by  the 
General  Electric  Co., 
nake  connections  Iron) 
automatic  regulator 
panel  as  shown  below 


FIG.  416. 

lever  back  and  forth.  This  lever  engages  a  suitable  pawl  and 
ratchet  mechanism  so  arranged  that  when  the  electro-magnetic 
scale  is  not  in  balance,  it  releases  one  of  two  pawls  which 
then  catches  the  teeth  of  a  wheel,  and  causes  it  to  revolve  in 
one  direction  or  another,  by  the  aid  of  the  pendulum  motion  of 
the  lever,  carrying  the  pawls,  at  the  same  time  the  shaft  of 


ARC  FURNACES  IN  GENERAL 


105 


this  latter  wheel  carries  the  switch,  which  operates  the  driving 
motor. 

The  electro-magnetic  scales,  which  bring  about  the  desired 
regulation,  are  built  for  either  direct  or  alternating  current. 
It  operates  as  a  volt,  ampere,  watt  or  ohm  meter  and  is  pro- 
vided with  a  regulating  resistance,  which  allows  the  operating 
conditions  of  the  furnace  to  be  changed  at  will.  The  double- 


FIG.  42. 

throw  switch  which  controls  the  driving  motor  is  either  single 
or  double  pole.  The  current  is  broken  between  an  adjustable 
copper  piece  and  a  block  of  carbon  of  generous  dimensions  so 
as  to  equalize  the  burning  away  of  the  contacts  or  to  lengthen 
the  time  of  contact 

If  several  furnaces  are  to  be  automatically  regulated,  only 
one  driving  motor  is  required  for  all  regulators.  The  apparatus 
are  then  mounted  on  a  switchboard,  which  also  carries  the  con- 
trol instruments,  such  as  volt  and  ammeters. 


IOC     ELECTRIC  FURNACES  IN    THE  IRON  AND  STEEL  INDUSTRY 

The  regulators  are  also  provided  with  a  manually  operated 
switch,  which  cuts  out  the  automatic  regulation,  so  that  hand 
regulation  may  be  resorted  to.  The  motor  drive  for  the  pulleys 
is  kept,  however,  which  is  often  very  desirable  when  using  hand 
regulation.  There  is  a  train  cf  gears,  of  which  a  pinion  and 


FIG.  43. 

rack  either  raises  or  lowers  the  electrodes.  The  electrodes  may 
also  be  suitably  set  by  the  aid  of  cables  or  chains.  The  weight 
of  the  electrode  and  its  appurtenances  may  be  partly  equalized 
by  a  suitable  counterweight. 

The  new  Type  B  regulator  here  shown,  Figs.  42  and  43,  is 


ARC  FURNACES  IN  GENERAL  107 

an  improvement  over  the  old  type  Thury.  In  the  old  model 
many  of  the  parts  subject  to  wear  became  out  of  adjustment, 
and  to  obviate  this,  all  parts  which,  when  worn,  throw  the 
machine  out  of  adjustment,  have  been  eliminated,  thereby 
making  the  new  regulator  better  than  the  older  type. 

Some  of  the  more  important  changes  are  as  follows:  The 
reciprocating  motion  is  now  obtained  by  means  of  a  set  of 
spiral  gears  operating  a  crank  pin  and  block,  which  latter  slides 
between  two  guides  connected  to  the  rocking  lever.  This 
principle  of  motion  brings  the  movement  in  a  direct  vertical 
line  so  that  wear,  if  any,  is  equally  divided  and  the  dogs  will 
always  engage  in  the  ratchet  wheel. 

The  entire  movement  is  enclosed  in  a  gear  box  and  runs  in 
oil,  so  that  wear  is  reduced  to  a  minimum.  The  gears  have  a 
ratio  of  about  2^:  i  and  the  driving  shafts  of  each  regulator 
are  coupled  together  by  means  of  a  flexible  coupling.  This 
shaft  replaces  the  countershaft  and  pulleys  of  the  old  type.  The 
carbon  contacts  have  been  replaced  by  copper  contact  fingers, 
so  arranged  as  to  have  a  good  wiping  contact,  each  contact 
being  provided  with  blowout  coils.  The  neutralizing  arm  is 
now  made  straight  and  provided  with  pivot  screws  to  take  up 
wear.  The  knife  which  engages  the  pawls  is  so  arranged  that 
coarse  or  fine  regulation  can  be  obtained  with  very  little  trouble. 

All  parts  requiring  adjustment  have  been  made  easy  of 
access.  The  whole  apparatus  is  built  upon  a  panel  and  units 
can  be  added  as  desired.  The  units  are  enclosed  in  a  fire-proof 
steel  case  and  this  is  mounted  on  a  pipe  structure  which  also 
carries  the  rheostats  and  controllers. 

The  foregoing  has  briefly  discussed  the  more  or  less  common 
phenomena  and  appliances  of  arc  furnaces,  and  hereafter  some 
of  the  various  designs  of  arc  furnaces  will  be  gone  into.  The 
most  important  things  of  arc  heating  may  again  be  briefly 
stated  here. 

In  all  arc  furnaces  the  heating  of  the  bath  is  brought  about 
practically  exclusively  by  the  arc  itself.  There  are  always  tem- 
peratures of  about  3500°  C.,  occasioned  by  the  arc.  Even  with 
a  moderate  heating  this  temperature  cannot  be  avoided. 


108    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Borchers,  in  his  1908  address  before  the  "Verein  deutscher 
Eisenhiittenleute,"  said  about  this: 

"In  arc  furnaces  there  may  be  many  arcs,  the  arcs  may  also  be  brought 
in  more  or  less  great  distances  from  the  bath,  in  order  to  bring  this  to  a  tem- 
perature of  less  than  3500°  C.,  but  3500°  C.  is  always  generated  at  some 
restricted  places,  and  we  must  operate  downwards  from  this  temperature." 


IT-S.P.Switch 
TR-Furnace  Operating 

Mech 
MT-MotorOpera 

Furnace 

PT— Power  Trans 
former 


R- Regulator 
S- Solenoid 
CR-Auto  Device  Contacts 
IG-Main  D.P.Switch 
CG -Fuses 

RP-Motor  Rheostat 
C- Controller 
R  A- Regulator  Rheostat 
F  —  Electric  Furnace 
I  M-D.P.Motor  Switch 
CM -Motor  Fuses 
MR-Motor  Driving  Auto  Reg-. 
T-Current  Transformer 
A  —Ammeter 


FIG.  430. — Connections  of  Thury  regulating  system. 

The  automatic  electrode  regulation  brings  with  it  decided 
advantages,  all  of  them  tending  to  reduce  the  cost  of  opera- 
tion and  increase  the  daily  tonnage.  This  is  apparent  when 
it  is  considered  that  a  well-designed  machine  operates  with 
greater  regularity  than  a  man,  needing  only  a  little  oil,  an 
occasional  adjustment,  and  the  replacement  of  a  small  part 
now  and  then,  in  order  to  have  it  function  properly,  whereas 
a  man  does  not  always  feel  the  same  on  Saturday  night  as 


ARC  FURNACES  IN  GENERAL  109 

on  Monday  morning.  The  kw.-hrs.  per  ton  are  less,  the 
refractories  last  longer,  the  electrode  consumption  is  less,  the 
overhead  charge  diminishes  as  the  output  increases — and  all  of 
these  advantages  for  only  $2,500  more  per  furnace.  Even 
though  the  increased  output  is  only  5  or  10% — sometimes  it  is 
more — the  advantage  of  having  automatic  electrode  control  is 
well  recognized,  and  is  found  on  practically  all  arc  furnaces 
to-day,  excepting  some  of  the  smaller  ones  of  }4-ton  or  less 
capacity  ptr  heat. 

REFERENCES 

"  Laws  of  Electric  Losses  in  Electric  Furnaces."  Transactions  A.  E.  S. 
1909.  P.  265.  Hering. 

"  Determinations  of  the  Constants  of  Materials  for  Electrode  Losses," 
Transactions  A.  E.  S.  1910.  P.  151.  Hering. 

"  Design  of  Furnace  Electrodes,"  Electrical  World.  June  16,  1910. 
Hering. 


CHAPTER  VII 
THE  STASSANO  FURNACE 

IT  was  shown  in  Chapter  VI,  that  among  the  better  known 
electric  furnaces,  the  Stassano  and  Rennerfelt  furnaces  are  the 
only  ones  which  are  exclusively  operated  by  arc  heating.  We 
may,  therefore,  also  refer  to  them  as  radiating  arc  furnaces. 

It  was  Stassano'- 's  original  ambition  to  build  an  electric  blast 
or  shaft  furnace.  His  object  was  primarily  to  use  profitably  the 
rich  ore  fields  of  Italy,  where  native  coal  is  scarce. 

His  first  patent,  issued  in  1898,  in  England,  is  based  on  the 
following  claim:  "The  utilization  of  caloric  energy  of  the 
voltaic  arc  for  primary  determining  the  reduction  of  oxide  of 
iron  and  the  metals  to  be  combined  therewith  and  afterwards 
melting  the  metallic  masses  reduced,  for  the  purpose  of  obtaining 
in  a  fluid  state  the  product  desired,  all  substantially  as  set  forth." 

The  furnace  which  Stassano  suggested  for  this  trial  is  shown 
by  Fig.  44  in  plan  and  vertical  cross-section.  Without  describ- 
ing the  first  design  of  this  furnace  at  length,  it  may  be  briefly 
said,  that  Stassano  laid  great  stress  on  the  point  that  no  air  was 
permitted  to  enter  the  furnace.  With  a  furnace  of  this  kind 
Stassano  made  his  first  tests  in  Rome.  With  1800  amperes  at 
50  volts  he  succeeded  in  producing  30  Kg.  (66  Ibs.),  of  metal  in 
one  hour. 

As  a  result  of  these  trials,  a  furnace  plant  for  the  direct 
reduction  of  iron  ores  was  erected  at  Darfo,  in  Lombardy,  Italy. 

Despite  several  changes  in  the  construction  of  his  furnace, 
Stassano,  though  keeping  his  method  of  heating,  was  not  able  to 
give  any  permanent  life  to  his  electric  shaft  furnace.  When  the 
Canadian  Commission  made  their  observation  trip  in  1904  the 
installation  at  Darfo  was  no  longer  in  existence. 

In  the  meantime,  Stassano  had  forsaken  the  original  design 
of  the  shaft-like  construction,  and  instead  built  a  hearth  furnace 

110 


THE  STASSANO  FURNACE 


111 


with  an  inclined  bottom  as  shown  in  Figs.  45  and  46.    This 
furnace  in  which  the  ore  was  charged  underneath  the  arcs,  in- 


FIG.  44. 


FIG.  45. 


stead  of  at  the  top,  as  in  his  shaft-like  furnace,  was  intended  for 
both  the  reduction  of  iron  ores  to  pig  iron,  and  the  refining  of 


112  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

pig  iron  to  steel.  As  the  figure  shows,  the  furnace  was  meant 
to  have  three  pairs  of  electrodes,  which  could  all  be  used  at  once, 
or  singly,  for  striking  the  arc,  so  that  the  temperature  of  the 
furnace  could  be  regulated. 

But  even  with  this  suggestion  for  a  pure  arc  furnace  Stassano 


FIG.  47. 

could  not  achieve  success.  He  was  however  able  to  make  a 
new  furnace  installation  at  Turin,  Italy,  in  which  he  first  used  a 
rotating  furnace.  This  furnace  was  patented  in  all  industrial 
countries,  and  dated  about  the  year  1902.  As  this  furnace  is 
in  use  to  some  extent  today,  it  will  be  discussed  in  detail,  showing 
as  it  does  the  first  known  furnace  with  purely  arc  heating. 


THE  STASSANO  FURNACE 


113 


Figs.  47  and  48  show  the  furnace  in  vertical  and  horizontal 
cross-section.  It  is  very  evident  from  the  claim  of  Stassano's 
patent  that  he  laid  particular  stress  on  the  motion  of  the  molten 
metal  in  the  furnace. 

As  the  drawings  show  (Figs.  47  and  48),  the  rotary  arrange- 
ment of  the  furnace  necessitates  a  vertical  cylinder.  The  shell 
of  the  furnace  is  constructed  of  sheet  iron,  and  is  connected  at 
the  lower  part,  near  the  bottom,  with  a  strong  ring-shaped  carrier, 


FIG.  48. 

which  in  turn  rests  on  rollers.  The  motion  is  usually  transmitted 
by  gears  driven  by  an  electric  motor.  At  the  middle  of  the 
furnace  bottom,  axial  to  the  direction  of  the  furnace,  we  find 
the  current  and  water  supply.  The  current  is  brought  in  by 
means  of  brushes  and  slip  rings,  such  as  are  found  on  any  poly- 
phase motor.  The  water  cooling,  which  is  brought  from  the 
fixed  to  the  movable  part  by  suitable  means,  is  needed  for  two 
purposes  with  this  furnace.  First,  it  serves  as  cooling  water 
for  the  electrodes,  and  again  as  the  water  under  pressure  for  the 


114    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

electrode  regulation.  The  figures  show  that  the  furnace  hearth 
is  covered  with  a  double  sort  of  roof,  which  is  not  readily  re- 
movable with  this  type  of  furnace.  This  arrangement  allows 
the  heat  protecting  qualities  of  the  brickwork  to  be  utilized  to  a 
great  extent,  and,  as  a  matter  of  fact,  this  method  is  said  to  give 
an  extraordinary  heat  insulation,  which  can  even  be  bettered 
by  inserting  layers  of  lime  or  sand. 

Fig.  47  shows  an  outlet  in  the  upper  part  of  the  melting 
chamber,  allowing  a  free  escape  of  the  gases  which  are  generated 
during  the  reaction.  This  outlet  pipe  is  surrounded  with  a  sand 
filled  covering,  into  which  it  dips  at  its  lower  end.  This  pipe 
does  not  take  part  in  rotation  of  the  furnace,  but  is  kept  in  place 
by  suitable  means. 

The  gas  removing  system  again  betrays  the  ambition  of 
Stassano  to  smelt  ore,  and  serves  to  protect  the  furnace  com- 
pletely from  the  entrance  of  outside  air.  As  a  matter  of  fact, 
however,  this  furnace  did  not  give  satisfactory  results  for  smelting 
ores  directly.  On  this  account  this  furnace  is  today  used  only 
for  the  working  up  of  scrap  or  for  refining  hot  charges. 

In  such  cases,  therefore,  this  gas  flue  falls  away,  as  in  the  in- 
stallation of  duplicate  Stassano  furnaces  at  the  Bonner  Maschin- 
enfabrik,  Bonn,  Germany.  The  hearth  here  has  also  been  given 
a  hexagonal  shape,  whereas  Fig.  48  still  shows  the  round  form 
as  used  by  Stassano. 

The  bottom  of  the  furnace  consists  of  Magnesite  brick,1 
as  does  also  the  double  form  of  furnace  roof.  The  insulating 
layers  of  furnace  refractories  are  partly  comprised  of  tamped  in 
material.  The  furnace  is  provided  with  a  door  for  watching  the 
metallurgical  work,  for  charging  the  metal,  adding  the  slagging 
materials  and  rabbling  it  off,  for  taking  samples,  etc.  Besides 
this  the  furnace  bottom  is  supplied  with  a  tap,  through  which 
the  finished  material  flows. 

The  most  essential  and  most  important  furnace  part  is,  of 
course,  the  arrangement  of  the  electrodes.  As  the  furnace  may  be 
built  as  well  for  single  phase  as  for  three  phase,  it  would  have 

1  According  to  Stahl  und  Risen,  page  1066,  1910,  the  side  walls  and  bottom 
are  said  to  have  lately  consisted  of  tamped  in  dolomite. 


THE   STASSANO  FURNACE  115 

two  or  three  electrodes,  as  the  case  may  be.  These  pierce  the 
furnace  walls  as  is  plainly  shown  in  Figs.  47  and  48  and  form 
an  arc  or  arcs  in  the  middle  of  the  furnace  which  heat  the  bath. 

Stassano  laid  great  stress  on  the  design  of  bringing  the  elec- 
trodes through  the  furnace.  The  electrodes  enter  the  furnace  by 
first  piercing  double  walled  cylindrical  chambers.  There  is  a 
circulation  of  water  in  the  space  surrounded  by  both  walls,  in 
order  to  keep  the  temperature  of  the  outer  electrode  portion 
down.  There  is  a  regulating  cylinder  over  each  cooling  cylinder, 
the  former  aiding  the  setting  of  the  electrodes  to  any  desired 
point.  The  piston-rod  is  connected  at  its  outer  end  by  means 
of  a  sliding  guide  rod  with  the  one  end  of  another  rod,  which 
carries  the  electrode  itself  at  the  other  end,  which  latter  end  is 
in  the  cooling  cylinder.  In  order  to  better  show  this  arrange- 


FIG.  49. 

ment,  the  whole  design  of  this  electrode  regulating  apparatus  is 
shown  in  Fig.  49  on  a  larger  scale. 

The  regulating  of  the  electrodes  is  accomplished  without 
any  automatic  regulating  apparatus,  but  is  accomplished  manu- 
ally by  the  aid  of  the  hydraulic  cylinder.  Any  common  water 
pressure  of  4  or  5  atmospheres  (60  or  75  Ibs.)  can  be  used,  so 
that  no  special  water  pumps  are  needed  for  the  electrode  regula- 
tion. The  current  carrying  parts  are  naturally  easily  and  well 
insulated  electrically  from  the  furnace  shell,  as  short  circuits 
would  otherwise  occur  through  the  furnace  walls.  Stassano 
did  not  look  with  favor  upon  any  automatic  regulating  appa- 
ratus for  his  electrodes,  and  Osann  who  studied  the  operation 
of  the  Stassano  furnace  in  detail  gave  the  following  reasons  in  a 
report  in  Stahl  und  Eisen,  1908:  "An  automatic  regulating 


116     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

arrangement  would  be  complicated  in  any  event  and  would  not 
be  advisable  if  for  no  other  reason  than  this  alone  because  the 
electrodes  are  withdrawn  while  charging;  besides  this,  an  elec- 
trode breaking  off  now  and  then  is  not  precluded,  and  this  frag- 
ment must  be  removed  quickly.  This  is  simply  and  quickly 
accomplished  by  calling  to  the  man  who  watches  the  three 
ammeters,  and  operates  the  three  corresponding  levers  which 
control  the  hydraulic  cylinders  for  the  electrodes.  The  electrodes 
can  be  used  up  until  the  remaining  stump  only  protrudes  .1  m. 
(4  inches).  Then  they  are  changed,  and  this  change  takes  only 
from  3  to  5  minutes,  all  of  which,  I  have  personally  assured 
myself." 

We  now  come  to  the  behavior  of  the  furnace  during  its 
operation.  As  already  mentioned,  the  electrodes  are  withdrawn 
when  the  furnace  is  being  charged.  When  the  furnace  is  about 
two-thirds  charged,  the  electrodes  are  brought  together,  to 
again  form  arcs  and  are  then  regulated  by  watching  the  needles 
of  the  ammeters.  The  charging  of  the  furnace  with  scrap  takes 
about  15  minutes  for  a  i-ton  furnace,  and  the  setting  of  the 
electrodes  thereafter,  takes  about  two  minutes.  As  soon  as  the 
first  scrap  is  melted  down,  the  remainder  is  charged  on  top  of 
it,  but  this  time  without  withdrawing  the  electrodes,  i.e.,  without 
any  interruption  of  the  current  taking  place  and  working  with 
the  utmost  speed,  so  as  to  avoid  all  radiating  losses.  The  slag- 
forming  materials  are  charged  in  the  usual  way,  and  the  dephos- 
phorizing slag  is  likewise  removed  after  the  dephosphorizing 
period  is  over,  similar  to  the  practise  with  any  other  electric 
furnace.  In  order  to  easily  remove  the  slag,  the  furnace  is 
turned  far  enough  so  that  it  may  be  conveniently  removed 
through  the  door.  This  is  possible  as  the  furnace  axis  has  a  defi- 
nite angle  of  about  7°  from  the  vertical,  so  that  the  door  assumes 
different  positions  toward  the  bath  surface  during  the  turning. 

After  this  general  characterization  of  the  Stassano  furnace, 
we  turn  to  one  of  its  definite  examples,  viz.:  the  duplicate  furnaces 
at  Bonn  of  i-ton  size,  being  one  of  the  1910  Stassano  furnace 
installations. 

These  i-ton  furnaces  of  2 50- HP  are  built  for  three-phase 


THE   STASSANO  FURNACE  117 

current;  no  volts  is  needed  to  operate  them.  The  current  is 
supplied  from  a  distant  central  station  at  an  incoming  voltage 
of  5200.  This  voltage  can,  of  course,  not  be  used  directly  in  the 
Stassano  furnace,  and  is  consequently  transformed  in  a  separate 
transformer,  removed  from  the  furnace,  and  stepped  down  to  the 
aforesaid  no  volts.  During  the  normal  operating  condition, 
the  furnace  takes  from  1000  to  noo  amperes  at  105  to  no  volts, 
and  this  current  is  held  as  steady  as  possible  throughout  the  en- 
tire operation.  The  Stassano  furnace  having  a  very  good  power 
factor,  (as  high  as  .9  to  .95  per  cent.,)  the  energy  consumption 
for  this  i-ton  three-phase  furnace  is  1.73  X  noo  X  no  X  .95  = 
198.86  Kw.,  or  say,  200  Kw. 

It  is  necessary  to  have  a  man  watch  the  electrical  conditions. 
He  regulates  the  arcing  distances  of  the  electrodes,  by  means 
of  the  levers  controlling  the  hydraulic  cylinders,  and  watches 
the  ammeters,  one  of  which  is  in  each  phase.  The  rotating 
motion  of  this  Stassano  furnace  in  Bonn  is  transmitted  by  means 
of  a  5 -HP  motor  to  a  tight  and  loose  pulley,  connected  by  a 
shaft  to  gears,  one  of  which  is  a  part  of  the  furnace.  The  electrode 
diameters  of  all  Stassano  furnaces  are  kept  down  as  much  as  possi- 
ble, so  that  the  work  is  carried  on  with  comparatively  high  cur- 
rent densities.  In  furnaces  up  to  500  HP,  electrode  diameters  of 
80  mm.  (3.2  inches)  are  used.  According  to  an  article  by  Cous- 
sergues  in  the  Revue  de  Metallurgie,  this  diameter  is  also  used 
in  larger  furnaces  up  to  1000  HP.  In  this  case,  however,  the 
electrodes  are  doubled  in  number. 

Accordingly,  for  the  25O-HP  furnace  at  Bonn,  for  instance, 
which  takes  noo  amperes  with  its  80  mm.  (3.2  in.)  diameter 
electrodes,  whose  cross-section  is  5024  square  mm.  (7.78  sq.  in.) 
corresponding  to 

iioo  /noo        141  amps.\ 

—  =  .22  amperes  per  square  millimetre  (-^  =  per  sq  in  J 

or  22  amperes  per  square  centimetre. 

With  a  5oo-HP  furnace  having  the  same  electrode  cross- 
section  and  about  twice  the  current,  the  current  density  would 
rise  to 


118  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


2200  /22oo         282.  amps.N 

—  =  .44  ampere  per  square  millimetre^—  -»   per  sq   in  j 

or  44  amperes  per  square  centimetre. 

This,  therefore,  gives  current  densities  which  still  substanti- 
ally exceed  those  given  by  Hansen,  as  mentioned  on  page  91, 
even  though  these  values  had  to  be  designated  as  being  high 
enough.  We  have  also  then  with  Stassano  furnaces  to  figure 
with  a  substantial  heat  generation  in  the  electrodes.  A  short 
example  may  show  this. 

New  electrodes  for  a  250-!!?  furnace  have  a  length  of  1.5 
rnetres  (59  inches).  As  the  electrodes  wear  off  during  the 
operation,  we  may  figure  with  an  average  length  of  i  metre, 
(39!  inches).  If  we  insert  besides  this  the  operating  value 
for  the  resistance  of  carbon  per  cubic  centimetre,  as  given  by. 
Hansen  and  shown  on  page  76  to  be, 

Pi  =  .00183  °nms  Per  cubic  centimetre, 
we  obtain  the  resistance  of  the  electrode  as  being: 

r  =  pi —  where  /  and  q  are  in  centimetres  and  square  centi- 
metres respectively. 
Consequently : 

r  =  .00183  ~      ~  =  .0036  ohm. 
*  50-24 

The  drop  in  voltage  in  the  electrode  of  a  250-!!?  furnace  hence  is 
e  =  ir 

=  noo  X  .0036  =  3.96  say  4  volts. 
The  energy  transformed  into  heat  per  electrode  is  consequently 

A   =  ie  watts  =  noo  X  4  =  4400  watts, 

or  in  all  3  X  4400  =  13200  watts.  That  is,  with  a  total  energy 
absorption  of  200  kw.  for  the  furnace,  there  is  6.5  per  cent,  lost 
through  Joule  losses  (?  r)  in  the  electrodes  alone. 

Besides  the  transformation  of  electrical  energy  into  heat  in 
the  electrodes  as  just  described,  several  interesting  phenomena 
will  be  found  in  the  Stassano  furnace  as  shown  below. 

First  regarding  the  length  of  the  arc,  with  Stassano  furnaces 
with  voltages  of  no  up  to  a  maximum  of  150  volts,  this  distance 


THE   STASSANO  FURNACE  119 

at  first  is  about  10  cm.  (4  inches)  from  electrode  to  electrode. 
During  the  run,  however,  the  arc  distance  increases  up  to  a  length 
of  30  cm.  (about  12  inches).  This  considerable  lengthening  of 
the  arc  is  partly  accounted  for  on  the  one  hand  by  the  high 
temperature  of  the  furnace  atmosphere,  and  on  the  other  hand 
through  the  gasification  of  the  electrode  ends  caused  by  the  arcs 
between  them.  It  is  to  be  noticed  that  the  arc  sags  toward  the 
bath.  This  phenomenon  can  only  be  regarded  as  favorable  to 
the  heatiLg  of  the  metal  bath. 

We,  therefore,  find  with  the  Stassano  furnace,  an  increasing 
lengthening  of  the  arc,  as  the  temperature  of  the  furnace  atmos- 
phere increases.  The  risk  must,  therefore,  be  run  of  having 
the  arc  break  and  making  it  anew,  when  charging  the  furnace 
with  cold  material  which  cuts  the  arc.  On  this  account,  there- 
fore, particular  care  should  be  exercised  when  charging  the 
furnace,  entirely  independent  of  the  horizontal  arrangement  of 
the  electrode  rods. 

If,  notwithstanding  this  care,  the  arc  should  still  break,  then 
the  rise  of  the  furnace  temperature  is  interrupted  until  the  arc 
is  again  established.  Still  there  wou'd  be  no  complete  interrup- 
tion of  the  energy  absorption.  Thus,  according  to  Coussergues, 
when  visiting  the  Stassano  furnace  at  Bonn,  the  arc  was  inter- 
rupted, yet  300  amperes  per  phase  at  120  volts  were  still  taken 
up  by  the  furnace,  which  is  about  one-third  of  the  total  energy. 

This  energy  absorption  with  an  interrupted  arc  is  only  then 
possible,  if  the  refractories  are  heated  to  redness.  For  the  energy 
absorption  is  dependent  upon  small  arcs  establishing  themselves 
between  the  refractories  and  the  electrode,  which  carry  the 
current  from  the  electrode  to  the  magnesite  bricks,  after  the 
latter  have  become  conductors  of  the  second  class,  due  to  the 
high  temperature,  and  may  therefore  be  regarded  as  heating 
resistances  between  the  electrodes  (see  page  17). 

Finally  attention  may  be  drawn  to  the  capability  of  Stassano 
furnaces  to  be  heated  up  electrically,  since  the  charge  is  com- 
pletely independent  of  the  arc  formation.  In  this  way  the 
furnace  is  also  kept  up  to  temperature  during  any  shut-downs. 
This  is  accomplished  by  heating  up  for  a  quarter  of  an  hour  with 


120      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  arc,  followed  by  a  current  interruption  for  three-quarters  of 
an  hour. 

The  above  states  the  specific  characteristics  of  the  Stassano 
furnace.  We  now  come  to  the  comparison  of  the  Stassano  furnace 
with  the  ideal  electric  furnace,  for  which  the  requirements  were 
laid  down  in  Chapter  V.  Without  entering  into  a  discussion  of 
the  purely  metallurgical  questions  which  are  gone  into  in  detail 
in  Part  II  of  this  book,  we  may  say  the  following: 

The  first  requirement  stipulated  that  the  electric  furnace 
was  to  be  capable  of  being  operated  with  any  prevailing  alternating 
current  at  any  voltage  and  periodicity. 

This  requirement  is  met  by  the  Stassano  furnace  better  than 
by  any  other  of  the  well-known  arc  furnaces,  for  Stassano  furnaces 
are  built  for  single-phase  as  well  as  for  three-phase  current.  At 
the  same  time  any  prevailing  periodicity  may  be  used.  Opposite 
this,  the  necessity  of  transforming  the  voltage  to  that  required 
by  the  furnace  only  plays  a  secondary  part,  for  this  transforming 
takes  place  in  comparatively  inexpensive  stationary  transformers, 
which  hardly  call  forth  any  particular  vigilance,  considering 
their  great  operating  safety. 

The  second  requirement,  viz.:  the  avoidance  of  sudden  power 
fluctuations,  is  not  fulfilled  so  well  by  the  Stassano  furnace  as  by 
other  furnaces  of  the  radiating  arc  type,  especially  when  melting 
down  cold  scrap.  There  are  some  interruptions  during  the 
charging  period,  as  already  mentioned,  and  though  the  sustaining 
of  the  arc  is  in  no  way  influenced  by  the  melting  process,  yet,  as 
the  arc  has  no  inherent  characteristic  tending  toward  stability, 
but,  as  experience  has  shown,  has  current  surges  almost  con- 
stantly from  electrode  to  electrode,  so  that  the  attendant  regu- 
lating the  electrode  levers,  even  with  constant  attention,  makes 
20  to  30  regulations  per  minute.  Still  Stassano  furnaces  are 
more  often  connected  directly  to  transformers  only,  although 
there  have  been  cases  where  flywheel  generators  had  to  be 
installed  to  absorb  part  of  the  violent  power  fluctuations. 

We  now  come  to  the  third  point  in  which  an  easy  regulation 
of  the  current  is  demanded.  This  requirement  may  also  be  re- 
garded as  being  fulfilled,  as  voltage  regulation  simultaneously 


THE   STASSANO   FURNACE     "  121 

causes  a  regulation  of  the  energy  supplied  to  the  furnace,  which 
is  entirely  independent  of  such  energy  regulation  which  is  pro- 
vided by  different  settings  of  the  electrodes.  It  was  mentioned 
on  page  115  that  Stassano  avoided  every  automatic  regulation  of 
the  electrodes  with  his  furnaces,  which  would  still  offer  several 
advantages.  These  reasons  are  referred  to  again  at  this  time. 

The  requirement  under  4,  viz.:  a  high  electrical  efficiency, 
does  not  seem  to  be  so  completely  fulfilled.  We  have  already 
seen  that  the  high  current  densities  in  the  electrodes  lead  to  im- 
portant heat  losses,  and  it  does  not  seem  therefore  that  it  is 
possible  to  avoid  considerable  losses.  This  is  even  accentuated 
by  the  intensive  water  cooling  of  the  electrodes.  There  are  also 
heat  losses  due  to  the  arc  not  being  sufficiently  near  the  bath 
during  the  different  periods  of  the  melting,  the  arc  also  being  too 
far  away  when  making  less  than  a  full  charge;  thus  this  heat 
goes  to  the  side  walls,  but  particularly  to  the  roof.  That  this  loss 
is  not  inconsiderable  is  evidenced  by  the  short  life  of  the  roof, 
one  week,  even  with  the  best  operators  and  refractories  other 
than  carborundum.  Besides  these  losses  there  are  the  trans- 
former losses,  for  changing  the  voltage  to  the  desired  amount, 
for  which  about  3  per  cent,  of  the  total  energy  may  be  allowed. 

The  fifth  point,  viz.:  the  tilting  arrangement,  which  Stassano 
replaced  with  a  turning  one,  no  doubt  gives  his  furnace  certain 
advantages;  still,  compared  to  the  tilting  device,  his  solution 
can  hardly  be  regarded  as  a  particularly  happy  one.  The  turning 
or  rotating  structure  requires  a  really  complicated  mechanism. 
As  a  proof  of  this  it  is  only  necessary  to  refer  to  the  water  supply 
for  the  electrode  regulation  and  to  the  electrode  cooling.  En- 
tirely aside  from  this,  it  hardly  seems  advantageous  to  have  a 
tapping  hole,  instead  of  pouring  over  the  lip,  when  teeming, 
especially  when  heats  follow  each  other  quickly,  as  is  usually  the 
case  when  treating  hot  metal. 

Even  though  the  requirement  of  an  easily  surveyed  hearth 
seems  to  be  completely  fulfilled,  it  is  yet  to  be  observed  that  the 
almost  horizontal  arrangement  of  the  electrodes  makes  the  ful- 
filment of  the  seventh  requirement  so  much  harder.  For  the 
breakable  electrodes  with  their  comparatively  small  cross- 


122  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

sections  are  liable  to  crack  off  when  roughly  handled,  so  that 
the  metallurgical  operations  in  the  furnace  entail  great  attention 
and  not  a  little  dexterity.  Besides  this,  the  Stassano  furnace 
would  have  the  advantage  of  influencing  the  charge  the  least 
with  its  arc  heating,  in  case  electrode  breakages  could  be  avoided 
with  certainty,  as  the  carbon  vapor  from  the  electrodes  is  not 
directly  against  the  molten  metal.  Relative  to  the  avoidance 
of  every  under  or  over  heating  of  the  metal,  it  must  be  said  that 
the  influence  of  the  arc  heating  as  employed  by  Stassano,  i.e.,  by 
use  of  the  radiation,  is  the  mildest  way  in  which  arc  heating  can 
be  used  at  all,  as  the  direct  influence  of  a  heating  agency  of  3500° 
C.,  on  the  metal,  is  avoided. 

Without  discussing  the  purely  metallurgical  demands,  the 
fulfilment  or  non-fulfilment  of  which  can  be  readily  seen  by  the 
construction  of  the  furnace,  we  find  that  the  requirement  of  a 
sufficient  but  not  too  strong  a  circulation  of  the  bath  is  fulfilled  by  the 
rotary  arrangement  of  the  furnace.  No  other  mechanical  cir- 
culation appears  in  the  Stassano  furnace  as  it  is  built  today,  and 
it  seems,  therefore,  that  if  any  security  is  desired  for  a  complete 
uniformity  of  the  material  in  its  several  layers,  it  is  not 
possible  to  dispense  with  the  mechanical  bath  circulation.  And 
these  necessary  mechanisms  must  always  be  designated  as  being 
very  complicated  (for  any  such  metallurgical  apparatus  as  this), 
no  matter  how  ingeniously  the  design  may  have  been  carried  out. 

Besides  the  many-sided  applications  of  this  furnace,  it  would 
seem  desirable  if  they  could  be  built  of  any  possible  size.  The 
proof  of  this  is,  however,  yet  to  be  established.  For  even  though 
Stassano  furnaces  of  5-ton  size  were  operated  by  Stassano  him- 
self, at  the  plant  in  his  charge  in  Turin,  the  plant  unfortunately 
has  been  shut  down.  It  may,  therefore,  at  present  only  be 
regarded  as  proven  that  the  Stassano  furnace  of  600  to  1000 
Kg.  (5/8  to  i  ton),  as  it  is  operated  at  Bonn  for  melting  up  scrap 
for  steel  castings,  succeeded  in  giving  good  results.  The  furnace 
does  not  seem  suitable  for  larger  sizes,  as  the  sensitive  devices 
permissible,  at  any  rate,  with  small  furnaces,  while  easy  to 
watch,  are  hardly  applicable  with  large  furnaces.  The  high 
current  density,  with  which  5-ton  furnaces  are  to  be  operated, 


THE    STASSANO    FURNACE 


123 


also  seems  unadaptable,  while  with  still  larger  furnaces  where 
the  doubling  of  the  electrode  number  would  be  encountered, 
difficulties  could  be  expected  from  the  simultaneous  manual 
regulation  of  six  electrodes. 

Larger  furnaces  would  have  longer  and  consequently  more 
breakable  electrodes,  which  would  otherwise  need  much  room 


124    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

during  the  furnace's  rotation.  Finally,  the  easy  working  of  the 
furnace  becomes  difficult  with  the  six  horizontal  electrodes 
over- topping  the  bath.  All  these  reasons  make  it  appear  that 
the  Stassano  furnace  in  its  present  customary  form  is  only 
useful  for  small  capacities. 

The  requirement  of  a  good  thermal  efficiency  is  acceptably 
fulfilled.  For  even  though  the  Stassano  is  the  electric  furnace 
where  the  metal  is  heated  most  indirectly,  but  where  the  atmos- 
phere directly  above  the  bath  is  heated  the  strongest,  and  though 
it  is  not  possible  to  avoid  a  considerable  heat  loss  when  the 
furnace  door  is  opened,  still  it  is  well  to  note  that  the  heat  in- 
sulation with  the  Stassano  furnace  is  extraordinarily  well  carried 
out,  and  that  consequently  it  is  possible  to  attain  satisfactory 
power  consumption  figures  for  melting  a  ton  of  steel.  And  these 
vary  between  800  and  1000  Kw.  hours  per  ton  of  steel  for  melting 
cold  stock  for  making  steel  castings. 

According  to  Osann  (Stahl  und  Risen,  1908,  p.  660),  we 
find  that  he  begins  with  a  cost  of  62  cents  for  electrodes  at  the 
Bonn  furnace  and  $2.75  for  refractories  per  ton  of  steel,  so  that 
we  cannot  speak  here  of  exactly  low  refractory  costs,  which  could, 
however,  be  considerably  reduced  by  using  dolomite  bottoms  and 
side  walls  (Stahl  und  Eisen,  1910,  p.  1060). 

The  installation  costs  for  a  i-ton  furnace  are  given  by  Osann, 
inclusive  of  switchboard  and  foundation,  at  $8,750.  This  does 
not,  however,  say  that  the  cost  of  the  necessary  transformer  is 
included  in  this  price.  In  Bonn  the  voltage  is  stepped  down 
from  5200  to  no  volts.  On  the  other  hand,  it  may  be  said  that 
at  Bonn  they  were  enabled  to  connect  to  an  existing  central 
station,  so  that  in  case  such  connection  is  not  possible,  the 
installation  cost  would  be  increased  by  an  amount  equal  to  the 
cost  of  an  isolated  plant  (250  HP  for  a  i-ton  furnace). 

Fig.  50  shows  a  Stassano  furnace  from  which  the  general 
arrangement  is  evident.  Regarding  the  sale  which  these  furnaces 
have  had,  reference  is  given  to  the  list  in  Chapter  XV.  The 
giving  of  licenses  for  Stassano  furnaces  is  made  by  the  Banner 
Maschinenfabrik  und  Eisengieszerei  Fr.  Mb'nkemoller  &  Co., 
Bonn  on  the  Rhine,  Germany. 


CHAPTER  VIII 

THE   HEROULT   FURNACE 

HEROULT  had  already  earned  great  merit  in  the  development 
of  electro-metallurgy,  on  account  of  his  electric  furnace  for  the 
production  of  aluminum.  He  was  the  first  to  discover  how  to 
build  an  arc  furnace  for  refining  iron,  having  vertical  electrodes 
pointing  directly  at  the  bath.  Before  this  these  furnaces  had 
the  objection,  that  the  iron  bath  greedily  absorbed  the  carbon 
from  the  immersed  electrodes.  On  July  4,  1900,  Heroult  made 
the  suggestion  (see  German  patent  No.  139904),  that  to  avoid 
the  absorption  of  carbon  by  the  metal  bath,  the  slag  used  to 
refine  the  metal  should  be  inserted  between  the  bath  and  the 
electrode. 

According  to  the  patent  description  the  electrodes  are  to  be 
so  far  separated  from  each  other  and  are  to  dip  so  little  into  the 
slag,  that,  on  the  one  hand,  the  resistance  between  the  electrodes 
within  the  layer  of  slag,  shall  be  great  enough  to  force  the  current 
from  the  one  electrode  through  the  slag  lying  directly  beneath 
it  to  the  metal,  and  from  the  metal  again  through  the  same  layer 
of  slag  to  the  other  electrode,  and  that  there  shall  be  otherwise 
no  connection  between  either  electrode,  and  the  metal.  Further, 
according  to  the  patent  description,  the  striking  of  arcs  between 
the  electrodes  and  the  metal  bath  into  which  the  electrodes 
project,  is  not  precluded,  or  is  it  necessary.  Regulating  the 
distance  between  the  electrodes  and  the  metal  bath,  however,  is 
the  important  part.  This  must  be  accomplished  in  such  a  way 
that  the  slag  layer  between  the  electrodes  and  the  metal  bath 
remains  hotter  and  more  conductive  during  the  entire  refining 
period,  than  the  layer  of  slag  between  the  electrodes,  because 
only  in  this  way  will  the  current  take  the  path  as  prescribed 
above. 

125 


120    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

After  this  general  characterization  of  the  Heroult  furnace, 
and  before  entering  into  details  regarding  its  construction  and 
operation,  we  will  give  a  short  survey  of  the  development  of  this 
furnace. 

According  to  the  Electrochemical  and  Metallurgical  Industry, 
1909,  p.  261,  Heroult,  in  his  first  efforts  in  building  an  electric 
furnace,  leaned  narrowly  toward  his  type  of  aluminum  furnace. 


FIG.  51. — Five-ton  Electric  Furnace. 

In  this  furnace,  as  is  well  known,  one  pole  consists  of  a  hanging 
carbon  electrode,  while  the  other  pole  was  made  by  the  furnace 
hearth  itself.  For  this  purpose  the  hearth  was  made  of  carbon. 
When  it  was  necessary,  however,  to  obtain  a  material  with  the 
lowest  possible  carbon  content,  this  style  of  furnace  could  no 
longer  be  used,  as  the  carbon  of  the  hearth  bottom  was  greedily 
absorbed  by  the  molten  metal. 

On  that  account  Heroult  next  made  tests  with  a  furnace  for 
the  production  of  low  carbon  ferro  chromium.  The  bottom  of 
this  furnace  consisted  of  chromite  bricks  in  the  middle  of  which 
a  carbon  block  was  inserted  which  then  acted  as  the  bottom 


THE  HEROULT  FURNACE 


127 


electrode.  With  this  method  Heroult  hoped  that  a  part  of  the 
carbon  block  would  be  absorbed  by  the  molten  metal  and  that 
the  molten  mass  would  continue  to  force  its  way  down  absorbing 
carbon  as  it  went,  until  the  exterior  radiation  of  the  molten 
metal  would  cause  it  to  freeze  on  the  carbon  block.  Heroult 
hoped  to  keep  this  condition  constant,  so  that  there  would  be  an 
interposition  of  the  frozen  metal  between  the  bottom  carbon 


FIG.  52. 

electrode  and  the  bath,  which  would  at  the  same  time  prevent 
any  carbon  absorption  by  the  bath. 

But  the  tests  as  carried  out  did  not  fulfil  his  hopes,  and  so 
after  further  trials  there  was  produced  the  Heroult  furnace  as 
we  know  it  today.  This  has  been  characteristically  shown  by 
the  above  examples,  taken  as  they  are,  first  of  all,  from  the 
patent  records.  Furnaces  of  this  kind  were  first  put  in  trial  in 
Froges  and  La  Praz,  France. 

The  first  Heroult  furnace  in  Germany  was  installed  by  the 
firm  of  Richard  Lindenberg  of  Remscheid  in  1905,  and  put  in 
operation  in  February,  1906.  The  first  Heroult  furnace  in  the 
United  States  was  installed  by  the  Halcomb  Steel  Co.,  of 
Syracuse,  N.  Y.  Since  then  the  furnace  has  come  into  extensive 


128       ELECTRIC  FURNACES  IN  THE  IRON  AND   STEEL  INDUSTRY 

use,  thanks  to  its  simple  design,  and  thanks  to  a  thorough 
knowledge  of  the  metallurgical  operations,  which  have  been 
thoroughly  investigated  at  Remscheid,  and  elsewhere. 

Coming  now  to  the  furnace  itself,  we  may  say  the  following: 
Of  all  the  arc  furnaces  the  Heroult  furnace  resembles  most  nearly 
a  tilting  open  hearth  furnace.  It  consists  of  a  steel  plate  shell  of 
nearly  rectangular  but  sometimes  circular  form,  which  has  a 
rounded  bottom.  Fastened  on  this  are  pinions  which  permit  the 
furnace  to  roll  forward  on  a  rack  or,  in  later  designs  of  the  smaller 
size,  the  furnace  is  tilted  bodily  on  supports  hinged  near  the 


FIG.  53. 

spout.  The  furnace  is  tilted  either  by  means  of  "a  hydraulic 
cylinder  or  an  electric  motor,  which  latter  method  permits  the 
control  of  the  pouring  very  accurately.  In  the  case  of  both  the 
rolling  and  the  tilting  furnaces,  it  is  now  possible  to  pour  directly 
from  the  furnace  into  hand  ladles.  The  whole  design  of  the 
furnace  may  be  seen  by  consulting  the  Figs.  51  to  53  inclusive. 

The  lining  of  the  furnace  consists  of  fire-bricks,  which  are 
laid  directly  against  the  steel  plate  shell,  and  on  which  dolomite 
is  tamped,  with  the  exception  that  in  the  United  States  mag- 
nesite  is  generally  used  instead  of  dolomite  when  it  can  be  had- 


THE  HEROULT  FURNACE  129 

The  roof  is  removable  and  consists  of  a  steel  plate  frame  lined 
with  fire-brick,  the  former  also  having  convenient  screw  eyes 
so  that  the  entire  roof  may  be  readily  transported.  The  hearth 
may  be  easily  inspected  and  operated  during  the  charging 
period  as  the  furnace  has  from  2  to  4  doors,  according  to  its 
size,  one  being  over  the  spout.  As  the  metal  bath  is  needed  to 
conduct  the  electric  current,  the  current  is  shut  off  while  charging 
and  naturally  while  it  is  empty,  which  allows  the  refractories 
to  cool  off  somewhat. 

The  arched  roof  of  the  furnace  is  pierced  by  two  or  three 
electrodes.  Copper  cooling  chambers  are  placed  at  the  piercing 
points,  which  keep  the  carbon  electrodes  outside  of  the  furnace 
at  permissible  temperature  limits  (as  discussed  in  Chapter  VI), 
and  simultaneously  cool  the  brickwork  at  these  points.  Each 
electrode  hangs  from  a  right-angled  support,  which  is  movable 
in  a  vertical  direction  at  the  furnace.  This  support,  therefore, 
carries  a  rack,  which  is  moved  by  a  motor-driven  pinion.  The 
use  of  these  small  motors  in  this  design  permits  a  mechanical 
regulation  of  the  electrode  positions.  In  Remscheid  these  small 
regulating  motors  are  of  the  single  phase  zoo-volt  type.  These 
motors  operate  automatically  or  by  hand,  according  to  whether 
a  higher  or  a  lower  position  of  the  electrodes  is  called  for.  Nat- 
urally the  electrode  clamps  are  insulated  in  an  improved  manner 
from  the  furnace  casing. 

Regarding  the  development  of  the  automatic  regulating 
apparatus  of  the  Thury  system,  this  was  described  at  length 
in  Chapter  VI,  pages  102-104.  The  electro-magnetic  scales 
mentioned  there  are  connected  as  voltmeters  to  the  Heroult 
furnace  in  the  earlier  regulators,  as  shown  by  dotted  lines  of 
Fig.  54.  These  have  now  been  changed  to  ammeters,  so  that 
current  regulation  is  obtained  and  the  operation  of  the  furnace 
is  now  accomplished  with  more  ease.  One  regulator  is  pro- 
vided for  each  electrode.  With  the  earlier  designs,  the  voltmeter 
as  shown  in  Fig.  54  is  designated  by  m  in  whose  place  we  can 
imagine  the  electro-magnetic  scales.  Two  or  three  scales  are 
provided  as  each  electrode  is  regulated  separately.  The  scales 
are  influenced  by  the  voltage  which  lies  between  the  head  of  the 


130      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

electrode  and  the  bath,  which  receives  -the  main  current.  In 
order  to  obtain  this  voltage,  an  iron  rod  is  imbedded  in  the 
furnace  bottom,  which  in  turn  is  connected  to  the  remaining 
terminals  of  the  magnetic  scales.  These  scales  are  set  so  that  a 
difference  of  2  volts  from  the  normal  will  start  the  regulator 


FIG.  54. 

and  keep  it  as  near  constant  as  possible.  Lately,  as  the  majority 
of  the  furnaces  installed  are  fed  from  transformers  from  larger 
power  stations,  where  the  voltage  is  fairly  constant,  it  is  the 
current  that  requires  regulating  as  is  shown  by  diagram  of 
Fig.  430  of  Chapter  VI. 

The  design  of  the  furnace  is-  such  that  either  hot  or  cold 
charges  may  be  treated.  With  cold  charges,  however,  the 
current  fluctuations  are  still  heavy  until  the  whole  charge  is  melted 
down,  the  reason  being  that  it  is  much  harder  to  melt  down  a 
stone  cold  charge  in  a  Heroult  arc  furnace  and  maintain  the  arc 
than  it  is  to  treat  hot  metal.  This  is  not  only  because  this 
type  of  arc  furnace  always  operates  better  at  a  higher  temper- 
ature under  the  influence  of  which  carbon  evaporates,  but  also 
as  the  continuity  of  the  current  is  disturbed  with  cold  charging 
as  the  various  pieces  of  scrap  make  varying  and  imperfect  con- 
tacts here  and  there.  Furthermore,  the  appearance  associated 
with  the  so-called  over-regulation  causes  the  electrodes  to 
become  unruly  when  for  instance  the  heavy  current  fluctuations 


THE  HEROULT  FURNACE 


131 


occur  at  the  arc,  rupturing  and  re-establishing  itself.  During 
the  melting  of  a  cold  charge,  continuous  fluctuations  therefore 
follow  and  these  continue  until  the  charge  has  become  molten. 


FIG.  55. 

During  the  time  of  these  heavy  current  fluctuations,  that  is, 
while  melting  the  metal,  the  automatic  regulation  is  sometimes 
replaced  by  hand  regulation.  The  series  connection  of  the  carbon 
electrodes  has  a  negative  influence  on  the  electrical  condi- 


800  Kw. 


000 


3  A.M. 


2.A.M. 


FIG.  56. 


tions  even  with  a  perfectly  fluid  metal.  To  illustrate  this 
Fig.  55  shows  several  current  curves  as  they  were  recorded  by 
an  arc  furnace  with  series  connected  electrodes.  These  curves 


132      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

were  made  in  1909.  Other  curves  are  shown  in  Figs.  56  and  57, 
which  show  the  power  fluctuations  during  the  melting  and 
dephosphorizing  period  and  also  the  finishing  period  on  a  6- 
gross-ton  furnace,  operating  at  about  900  Kw.  More  lately 
these  furnaces  operate  with  about  1200  Kw.  Fig.  57  shows 
the  much  steadier  power  consumption  when  refining  hot  metal. 


At  present,  with  very  careful  charging  of  the  furnace,  it  is  pos- 
sible to  throw  on  the  automatic  regulators  simultaneous  with 
throwing  on  the  current.  This  reduces  the  current  fluctuations 
somewhat  as  shown  by  the  difference  in  the  power  fluctuations 
as  evidenced  by  Figs.  55  and  56,  the  latter  of  which,  also  57, 
were  made  in  1915. 

In  order  that  no  misunderstanding  may  arise  regarding  the 
heating  method  of  the  Heroult  furnace,  it  is  well  to  especially 
mention  at  this  time,  that  Heroult  had  soon  to  realize  that  he 
must  employ  an  arc  to  make  his  furnace  operate  even  though  it 
deviated  from  the  furnace  operation  of  his  patent  description. 


THE  HEROULT  FURNACE  133 

In  this  it  was  not  precluded  nor  was  it  necessary  that  arcs  should 
be  struck  between  the  electrode  and  the  bath.  Hence  to-day  the- 
furnace  voltages  are  chosen  so  high,  that  the  electrodes  are  set 
at  about  45  mm.  (1.8  in.),  above  the  steel  bath.  With  this  setting, 
it  is  possible  to  obviate  a  carburization  of  the  bath  when  the 
slag  is  interposed,  and  this  is  solely  caused  by  the  heating  action 
of  the  arc,  (having  a  length  as  mentioned  above,)  heating  the 
metal  to  the  desired  temperature. 

If  the  electrodes  in  the  Heroult  furnace  were  dipped  into 
the  slag,  so  that  no  arc  exists,  then  the  furnace  would  be  of  the 
pure  resistance  variety.  Should  we  now  calculate  the  resistance 
conditions  in  such  a  circuit,  we  shall  immediately  find,  that,  under 
these  conditions,  practically  the  whole  energy  would  be  changed 
into  heat  in  the  electrodes,  without  heating  the  bath  materially 
at  all.  This  is  apparent  when  we  compare  the  resistances  of  the 
two  carbon  or  graphite  electrodes  connected  in  series,  with  their 
comparatively  small  cross-section  and  very  great  length  and 
their  high  specific  resistance,  with  the  resistance  of  the  slag  layer 
and  the  bath  with  their  very  large  cross-sections  and  very  short 
lengths  and  the  very  low  specific  resistances  (at  least  as  far  as 
the  bath  is  concerned).  These  conditions  have  been  clearly 
recognized  by  the  representatives  of  the  Heroult  furnaces.  We 
quote  from  Prof.  Eichhoff  of  Charlottenburg,  the  technical 
adviser  of  Lichtenberg  of  Remscheid,  his  article  appearing  in 
Stahl  und  Eisen,  1909,  p.  843,  as  follows: 

"It  is  impossible  to  heat  an  arc  furnace  for  steel,  by  utilizing 
the  heat  generated  by  the  resistance  of  the  thin  slag  layer  or  the 
large  cross-section  of  the  bath.  These  resistances  only  furnish 
a  few  per  cent,  of  the  heat  necessary  in  the  furnace,"  and  again, 

"Obtaining  heat  by  the  rising  temperature  of  the  slag  with 
its  decreasing  resistance,  or  by  utilizing  the  resistance  of  the 
bath,  has  never  been  achieved,  simply  because  the  slag  layer  is 
too  thin,  and  the  cross-section  of  the  steel  bath  too  large.  Such 
a  view  therefore  is  a  fable,  which  I  oppose  from  the  start." 

This  description  should  suffice  to  give  a  perfectly  clear 
picture  of  the  workings  of  a  Heroult  furnace,  in  which  then 
practically  the  entire  heating  is  obtained  from  the  heat  of  the  arc. 


134  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

If  we  return  for  the  moment  to  the  furnace  design,  we  observe 
the  following:  The  Heroult  furnaces  were  first  built  for  single- 
phase  currents  for  from  25  to  33  cycles.  To-day  they  all  operate 
from  polyphase,  usually  3-phase  circuit  at  25,  50,  and  60  cycles. 
The  Heroult  furnace  at  La  Praz  operates  with  33-cycle  current 
at  no  volts,  single  phase.  The  charge  is  about  2^/2  tons.  At 
this  rate  the  furnace  consumes  about  4000  amperes.  Two  of  the 
i5-ton  Heroult  furnaces1  and  one  20- ton  are  operating  at  the 
works  of  the  Illinois  Steel  Co.,  South  Chicago,  and  another  at  the 
plant  of  the  United  Steel  Co.,  Canton,  Ohio.  The  hearth  of  this 
furnace  is  circular,  over  which  three  electrodes  are  arranged  at 
the  corners  of  an  equilateral  triangle.  One  of  these  furnaces 
is  operated  by  3-phase,  25-cycle  current,  delta  connection,  at 
i GO  volts.  Under  these  conditions,  the  current  per  phase  rises  to 
12000  amperes.  As  in  other  furnaces,  the  electrodes  are  auto- 
matically regulated.  The  current  is  taken  from  a  high-tension 
circuit  and  stepped  down  by  means  of  three  750  Kw.  transformers 
in  the  installation  at  South  Chicago  and  by  means  of  three  1000 
Kw.  transformers  with  the  Canton  furnace.  Accordingly  the 
former  1 5-ton  furnace  takes 

12000  X  100  X  1.73  =  2076  K.V.A. 

and  as  the  power  factor  is  between  .8  and  .9,  it  consumes  actually 
2076  X  .85  =  1760,  say  1800  Kw. 

The  difficulty  heretofore  in  building  large  arc  furnaces  has  lain 
in  the  inability  of  obtaining  a  large  electrode  that  was  durable 
in  service  and  not  having  too  great  electrical  or  thermal  losses. 
This  feature  will  be  alluded  to  later  on. 

In  order  to  give  an  idea  of  the  dimensions  of  the  electrodes  in 
Heroult  furnaces,  it  may  be  well  to  mention  that  the  electrodes 
carrying  4000  amperes  in  the  single-phase  furnace  operating  at 
La  Praz  have  a  cross-section  of  360  X  360  mm.  =  129,600  sq. 
mm.  (14.1  X  14.1  inches  =  200  sq.  in.),  and  a  length  of  1.70 

1  In  1912,  the  Metallurgical  and  Chemical  Engineering  reports  that  a  25- 
ton  Heroult  furnace  was  put  in  operation  at  the  Gewerkschaft  "Deutscher 
Kaiser,"  Bruckhausen,  Germany. 


THE  H^ROULT  FURNACE  135 

metres  (67  inches).  They  consequently  operate  at  a  current 
density  of 

129,600  /  200 

'  40QO     =32-4  sq,  mm.  per  amp.  \^^^  =  .05  sq.  in.  per  amp. 

4000  .    \ 

or  =  20  amps,  per  sq.  in.  1 

If  we  take  into  account  that  as  the  height  of  the  furnace  roof  over 
the  bath  is  70  cm.  (27^  inches),  and  the  clamping  length  at  the 
top  of  the  electrode  is  35  cm.  (13^  inches),  we  find  that  there  is 
a  certain  length  of  usable  electrode,  which  with  a  total  length  of 
1.75  metres  (69  inches),  makes  the  usable  portion  about  70  cm. 
(2 7//2  inches).  The  wwusable  portion  of  the  electrode  is  con- 
sequently about  i  metre  (39  inches). 

If  we  now  calculate  the  electrode  voltage  losses  in  accordance 
with  the  figures  just  mentioned,  similar  to  the  electrode  losses 
determined  for  the  Stassano  furnace,  we  obtain  the  following: 

Assume  specific  resistance  of  carbon  in  operative  condition  = 
pi  =  .00183  ohms  per  cubic  centimetre 

then  as  e  =  i  X  r,  where  r  =  p\ — ,  and  /  and  q  are  respectively 
in  centimetres  and  square  centimetres,  we  obtain — 

e  =  i  X  PI  X  —  =  4000  X  .00183  X  T  =  -565  volts. 

For  both  electrodes,  then  the  drop  is  1.13  volts,  because  they 
are  connected  in  series. 

The  result  as  figured,  however,  cannot  be  considered  as  correct, 
because  the  change  in  the  specific  resistance  with  increasing 
cross-section  was  not  taken  into  consideration.  In  the  calcula- 
tions, so  far,  we  kept  the  probably  correct  value  of  .00183  ohm 
per  cubic  centimetre,  which  is  in  keeping  for  an  electrode  of  80 
mm.  diameter,  whereas  the  electrode  of  the  Heroult  furnace  in 
question  corresponds  to  a  square  having  360  mm.  to  a  side.  If 
this  had  been  taken  into  consideration,  then  the  value  of  pi  =  .014, 
(when  following  the  values  given  on  pages  93-94),  should  have 
been  chosen  for  the  electrode  condition  in  its  cold  state.  Should, 
on  the  other  hand,  the  values  of  Hansen  be  taken,  where  the 


136  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

resistance  falls  to  about  40%  in  operation,  compared  to  the  cold 
resistance,  then  the  determination  should  have  been  figured  with 
PI  =  .0056  ohm  per  cubic  centimetre. 

Figuring  more  correctly  then  with  this  value,  we  obtain, 

e  =  4000  X  .0056  X         6    =  1.73  volts  per  electrode. 

The  drop  for  both  electrodes  is  consequently — 
2  X  1.73  =  3.5  volts. 

This  gives  a  loss  three  times  as  high  as  in  the  first  calculation. 
This  example  clearly  shows  of  what  importance  it  is  to  accurately 
know  the  different  constants  for  this  material  for  the  different 
cross-sections.  For  it  is  only  with  these  that  the  determinations 
of  the  conditions  arising  in  the  electrodes  can  be  figured. 

Of  course  it  is  not  to  be  supposed  that  this  last  value  gives 
a  final  idea  of  the  total  losses  in  the  electrodes,  because  in  the 
calculations  just  made  only  the  purely  electrical  losses  were 
judged.  This,  too,  with  the  rather  hazardous  assumption  that 
the  constant  taken  for  the  specific  resistance  of  the  carbon  elec- 
trode is  correct.  Meanwhile,  the  radiation  heat  losses  have  been 
entirely  disregarded.  It  is  undoubted,  that  the  latter  raises 
the  total  electrode  losses  considerably,  and  even  though  deter- 
minations regarding  radiation  heat  losses  are  hardly  possible, 
still  it  may  be  said  with  some  certainty,  from  measurements  of 
other  arc  furnaces,  that  the  total  electrode  losses  generally,  as 
well  as  in  the  Heroult  furnace  under  discussion,  will  not  be 
below  7  to  10%. 

These  losses  do  not  only  appear  of  this  value  in  the  compara- 
tively small  furnaces,  such  as  have  just  been  discussed,  i.e.,  of 
the  2-  to  3-ton  size,  but  especially  in  the  larger  sizes.  With  the 
size  of  the  furnaces  and  the  increasing  cross-sections  of  the 
electrodes,  the  difficulty  also  grows  of  obtaining  favorable  material 
constants,  which  is  a  thing  entirely  apart  from  the  difficulties 
to  be  surmounted  of  procuring  large  electrodes  of  considerable 
durability.  Chapter  VI  brings  out  these  details.  It  may  be  said 
further  regarding  the  practical  operation  of  the  15  and  25-ton, 
3-phast  curnaces  at  South  Chicago,  that  it  has  not  been  found 


THE  H^ROULT  FURNACE  137 

possible  to  increase  the  proportions  of  the  electrodes  at  will, 
but  lately  it  has  been  found  possible  to  obtain  an  electrode  of 
satisfactory  proportions  and  better  material.  As  has  been 
remarked  this  1 5-ton  furnace  operates  with  about  12000  amperes 
per  electrode.  The  conduction  of  such  currents  naturally  neces- 
sitates very  considerable  electrode  cross-sections.  It  was  at 
first  tried  to  produce  these  electrodes  in  single  large  blocks.  Ac- 
cording to  the  Electrochemical  and  Metallurgical  Engineering, 
1909,  p.  262,  one  of  these  block  electrodes  had  a  diameter  of  2  ft. 
(60.9  cm.),  by  a  length  of  ten  ft.  (3.048  m.}.  The  weight  of  one 
of  these  electrodes  was  about  3200  Ibs.  (1451.5  Kg.). 

The  results  with  these  colossal  electrodes  was  hardly  satis- 
factory, as  breaks  often  occurred  which  disturbed  the  operation 
of  the  charge  in  a  most  sensitive  way,  even  though  the  current 
density  operated  with  was  28  amperes  per  square  inch,  or  4.35 
amperes  per  square  centimetre,  corresponding  to  24  sq.  mm.  per 
amp.,  which  is  a  comparatively  high  density  in  spite  of  the  large 
electrode  cross-section.  (See  Chap.  VI,  page  82.)  On  that  ac- 
count they  sometimes  use  the  dearer  but  less  troublesome  graph- 
ite electrodes  instead  of  the  carbon  electrodes.  Quoting  from 
the  Metallurgical  and  Chemical  Engineering,  1910,  p.  179,  and 
following  pages,  we  find  that  the  electrodes  as  used  are  made  up 
of  Acheson  graphite  rods,  48  in. long  (12  2  cm.),  and  8  in.  (20.32011.) 
in  diameter.  Three  such  rods  are  butt-connected  to  a  total  length 
of  144  in.  (366  cm.),  and  three  such  144  in.  rods  are  arranged 
side  by  side  to  form  a  single  electrode,  consisting  (see  Fig.  60  a 
and  b)  thus  of  a  solid  bundle  of  three  rods,  each  144  in.  (366  cm.) 
long.  The  cross-section  is  therefore  3  X  50.2  =  150.7  sq.  in.  (3  X 
324  =  972  sq.  cm.).  The  consumption  of  these  electrodes  is  given 
as  averaging  6.6  Ib.  (3  kg.),  per  ton  of  steel,  and  this  figure  is 
stated  to  be  true  for  graphite  and  hot  charges. 

The  unavoidable  wearing  away  of  the  comparatively  dear 
electrodes,  naturally  causes  an  increase  in  the  steel  conversion 
costs,  which  is  hardly  desired.  In  the  beginning  there  were 
additional  losses  of  considerable  moment  which  had  to  be  reck- 
oned with.  These  were  caused  by  the  unusual  lengths  of  the 
electrodes  in  the  electrode  clamps  and  the  length  necessary  for 
the  distance  between  the  furnace  roof  and  the  slag  layer.  These 


138  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


costs  are  said  to  have  now  been  reduced  to  the  irreducible 
minimum,  by  using  the  otherwise  worthless  stub  ends  for  a  new 
electrode.  Figs.  58  and  59  show  two  possible  ways  in  which  the 
greatest  use  can  be  made  of  the  electrodes. 

Fig.  58  shows  the  electrode  made  from  shorter  pieces  with 
staggered  ends  held  together  with  graphite  screws.     This  method 
is  also  reported  to  have  been  used  with  the  15 -ton  furnaces  in  the 
United  States.     Fig.  59  shows  a  threaded  hole  in  the  end  of  the 
electrode.    On  the  one  hand  this  scheme  enables  the  conducting 
clamp  to  be  made  of  cast  copper,  as 
the  figure  shows,  whereas  otherwise, 
should  the  whole  electrode  become 
too   short,    it  can   be    unfastened 
at  the  copper  casting,  a  graphite 
screw  inserted  in  its  place,  and  a 
new   electrode   piece   screwed  be- 
tween the  too  short  electrode  and 
the  new  one.    This  is  also  evident 
from  a  view  at  Fig.  59.     The  latter 
way  of  lengthening  the  electrode  is 
now  in  general  use  all  over  the 
world.     It  seems  from   this   that 
the  possible  difficulties  due  to  the 
FIG.  58.         FIG.  59.  higher  resistance  at  the  points  of 

contact  are  not  so  great  as  might  be  expected  from  theoretical 
calculations,  especially  when  the  graphite  nipple  or  joint  is 
accurately  machined,  and  when  given  an  extra  y&  or  %  turn 
shortly  after  being  in  service. 

Following  this  it  may  be  well  to  relate  further  details  of 
the  operation  of  the  Heroult  furnace.  If  the  Heroult  furnace 
is  to  be  heated  up  after  putting  in  a  new  lining,  or  owing  to  the 
operation  being  interrupted  by  Sunday,  it  is  accomplished  by 
charging  the  furnace  with  some  coke,  which  acts  as  the  heating 
medium  and  at  the  same  time  as  the  conductor  from  one  electrode 
to  the  other,  (as  long  as  the  heating  of  the  furnace  is  accomplished 
electrically).  When  ready  to  place  the  furnace  in  operation, 
this  coke  is  raked  out  and  the  furnace  charged.  The  current 


THE  HKROULT  FURNACE  ]39 

is  then  switched  on  and  the  automatic  regulators  thrown  in  at 
the  same  time.  In  refining  molten  metal,  the  automatic  elec- 
trode regulators  are  thrown  in  at  once.  The  furnace  operation 
then  is  decidedly  smoother  than  when  melting  cold  scrap,  when 
hand  regulation  is  sometimes  resorted  to. 

As  with  all  other  electric  furnaces,  so  also  with  the  Heroult 
furnace,  we  find  that  the  power  consumption  varies  greatly  with 
the  size  of  the  furnace,  with  the  kind  of  charge  used,  and  the 
desired  quality  of  the  finished  material.  A  graphic  picture  of  the 
change  of  the  current  consumption  varying  with  the  size  of  the 
furnace  is  given  by  Fig.  60.  This  data  is  given  by  Eichhoff. 
Here  one  set  of  curves  represents  the  conditions  for  cold  and  one 
for  hot  charges.  In  the  upper  set  of  three  curves  the  lowest 
one  indicates  conditions  when  only  one  slag  is  used,  the  middle 
curve  when  two  slags  are  used,  and  the  highest  curve  when  three 
slags  are  used,  and  similarly  for  the  lower  set  of  three  curves. 
In  this  way  the  curves  show  a  rising  degree  of  purity  in  the 
metal.  The  table  accompanying  Fig.  60  gives  the  quantities 
directly.  Of  particular  interest  are  the  operating  figures  which 
have  been  achieved  with  the  1 5-ton  furnace.  According  to  the 
report  in  the  Metallurgical  and  Chemical  Engineering,  of  1910, 
p.  179,  ff.,  the  electric  furnace  is  charged  with  hot  metal  from 
the  Bessemer  converter. 

On  the  average  here  1 2  charges  are  made  daily,  with  an  average 
time  of  i  hr.  and  15  minutes  to  2  hrs.  and  15  minutes,  the  weight 
of  metal  averaging  from  12  to  14  tons.  The  average  consump- 
tion of  power  for  this  is  200  KW.  per  ton  of  steel  produced. 

If  we  now  pass  on  to  the  comparison  between  the  Heroult 
furnace  and  the  ideal  furnace,  we  come  to  the  first  demand  of  an 
electric  furnace,  that  every  existing  alternating  current  can  be  used. 
The  Heroult  furnace  fulfils  this  demand  only  in  part.  As  every 
arc  furnace  needs  a  certain  voltage,  the  Heroult  furnace  also 
demands  a  specific  potential,  so  that  in  nearly  every  instance  a 
stationary  transformer  becomes  a  necessity,  in  which  the  high 
pressure  of  the  distant  central  station  is  stepped  down  to  the 
desired  100  to  no  volts  at  the  furnace.  The  use  of  one  of  these 
transformers  is  almost  unavoidable  with  any  arc  furnace.  Other- 
wise, the  Heroult  furnace  can  use  any  existing  alternating 


140    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


THE  HEROULT  FURNACE  141 

current  of  any  commercial  frequency.  In  fact,  in  several  recent 
installations  a  power  factor  of  94  or  more  has  been  observed 
and  this  with  6o-cycle  current.  No  difficulty  has  been  found  in 
the  construction  of  the  furnace  with  three  electrodes,  in  furnaces 
from  the  largest  to  the  smallest  size. 

Up  to  the  present  time  the  avoidance  of  sudden  power 
fluctuations  has  not  been  attained  when  operating  Heroult 
furnaces.  At  present  the  Heroult  furnace,  with  its  electrodes  in 
series,  is  credited  with  having  almost  the  heaviest  power  fluctu- 
ations of  the  better  known  arc  furnaces.  However,  with  the 
improvement  in  the  automatic  regulation  and  the  handling  of  the 
furnace,  these  fluctuations  have  been  reduced  very  markedly 
and  this  without  the  introduction  of  reactance  coils  of  any  kind. 
(See  Figs.  55,  56,  57.)  This,  as  we  have  seen,  is  particularly 
so  when  melting  down  cold  stock.  The  conditions  are  more 
favorable  as  soon  as  the  charge  is  completely  melted,  or  when 
only  treating  hot  charges.  On  the  bath  of  these  hearths  three 
electrodes  appear  which  hinder  the  metallurgical  operations 
somewhat,  and  lead  to  greater  breakages  of  the  electrodes,  than 
two  electrodes  alone  would,  of  which  it  is  reported  that  breakages 
are  rare  during  operating.  In  addition  the  arrangement  of 
three  electrodes  requires  the  furnace  roof  to  be  pierced  three  times, 
which  seems  so  much  more  dubious,  as  the  flat  arched  roof  is 
subject  to  the  high  temperatures  of  the  arcs,  and  also  to  the  water 
cooling  around  the  three  electrodes,  so  that  inside  of  the  com- 
paratively small  space  of  the  furnace  roof,  we  have  several  large 
differences  of  temperature  arising,  which  naturally  tend  to 
weaken  and  destroy  the  roof.  Finally  it  must  also  be  mentioned 
that  three  electrodes  radiate  more  heat  due  to  their  larger 
surface  than  two  electrodes  do,  having  the  same  total  cross- 
section. 

Furnaces  which  are  operated  with  three  phase  current  con- 
sequently only  require  the  installation  of  stationary  transformers, 
as  the  central  station  is  usually  large  enough  nowadays  to  stand 
the  prevailing  power  fluctuations  of  arc  furnaces  of  this  type. 

Easy  regulation  of  the  power  is  present  in  the  Heroult  furnace, 
the  same  as  it  is  in  every  other  electric  furnace. 


142  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

In  judging  the  electrical  efficiency  of  the  furnace,  the  losses  in 
the  transformer  are  first  to  be  taken  into  consideration,  and 
then  the  losses  in  the  carbon  or  graphite  electrodes.  In  case  any 
rotary  transformers  have  to  be  used,  the  considerable  losses 
appearing  here  have  to  be  added.  Their  use  is  rare. 

In  order  to  give  a  probable  conception  of  the  electrical  losses 


SflHHBfil^^HBL. 

FlG.  6oa.  —Heroult  3-phase  furnace  of  15  tons  capacity.     Teeming  a  charge. 

the  efficiency  of  the  transformer  may  be  taken  as  about  96  to 
97%;  the  electrode  losses  at  about  10%,  of  which  at  least  3  to 
5%  are  purely  heat  losses,  and  in  case  rotating  transformers  have 
to  be  used  the  efficiency  of  these  machines  may  be  taken  at  about 
85%- 

The  further  requirements  of  a  tilting  furnace,  and  an  easily 
surveyed  and  accessible  hearth  are  fully  met. 

It  has  already  been  mentioned  in  which  way  Heroult  knew 


THE    HEROULT    FURNACE 


143 


144      ELECTRIC  FURNACES  IN  THE  IRON  AND   STEEL  INDUSTRY 

how  to  avoid  the  undesired  reducing  action  of  the  electrodes 
impinging  directly  on  the  metal.  It  is  to  be  noted,  however, 
that  this  reducing  action  cannot  be  altogether  avoided,  due  to 
the  electrodes  throwing  their  carbon  vapor  stream  against  the 
layer  of  slag,  even  though  the  slag  layer  protects  the  bath  from 
this  action.  The  prolonged  carbonizing  action  of  the  arc  furnace 
makes  more  difficult  the  oxidizing  processes;  for  instance,  during 
the  removal  of  the  phosphorous  it  cannot  be  without  its  influence 
on  the  time  of  treating  the  charge  and  the  power  consumption. 
When  removing  the  slag  it  is  well  to  consider  that  the  carbonizing 
action  of  the  arc  remains  the  same,  even  though  the  heating  is 
not  interrupted  during  this  period. 

If  we  now  take  up  the  requirement  of  the  motion  of  the  charge, 
we  find  that  from  reasoning  alone,  from  the  standpoint  of  purely 
thermal  action,  it  is  not  present.  For,  as  the  arc  operates  only 
on  the  surface  of  the  bath,  the  hottest  parts  of  the  bath  are  to  be 
looked  for  here.  On  account  of  the  electric  current,  on  the  other 
hand,  a  certain  motion  of  the  bath  takes  place,  as  this  current 
flows  through  the  electrodes,  and  a  part  of  the  bath  which  is, 
to  a  certain  extent,  a  moving  conductor  (as  the  motor  action  of 
the  electric  currents  acts  as  discussed  in  Chapter  III).  For,  in 
accordance  with  the  conditions  there  given,  the  bath,  or  the  part 
which  is  a  movable  conductor,  is  pushed  to  one  side,  so  that  the 
material  beneath  the  electrode  is  under  a  certain  magnetic 
pressure,  which  causes  a  certain  motion  in  the  bath  of  the  Heroult 
furnace.  With  all  this,  it  is  not  correct  to  assume  that  the 
motion  caused  in  the  bath  of  the  Heroult  furnaces  reaches  the 
bottom  of  the  bath. 

The  application  of  the  furnace  has  a  wide  scope,  due  to  the 
fact  that  it  works  as  well  on  cold  scrap,  but  with  heavier  power 
fluctuations,  as  on  hot  metal.  It  must,  however,  not  be  left 
unsaid  that  at  present  the  Heroult  furnace  is  the  only  one  that 
has  been  built  for  25  tons  and  actually  holds  28  tons,  which 
proves  the  adaptability  of  this  for  this  size.  Up  to  a  certain 
point  naturally  the  heat  losses  become  proportionately  smaller. 
However,  it  is  to  be  feared  that,  for  instance,  with  very  large 
arc  furnaces  with  three  electrodes  piercing  the  flat  arched  roof, 


THE  HEROULT  FURNACE  145 

that  this  would  cause  a  frequent  roof  renewal.  This  difficulty 
is  being  reduced  to  a  very  great  extent,  as  in  present  practice 
according  to  size  of  furnace,  whether  cold  or  hot  charging, 
silica  roofs  with  the  former  method  during  1916  lasted  respectively 
30,  47,  and  56  heats  in  a  two-ton  furnace,  whereas  with  the  larger 
furnaces  and  cold  charging  200  to  300  heats  have  been  reached 
before  complete  renewal  is  made.  In  these  cases  the  bottom, 
as  is  more  usual,  was  basic.  The  renewals  are  more  numerous 
with  3  holes  in  the  roof,  than  when  only  pierced  with  or  or  two 
electrodes,  other  things  being  equal,  owing  to  the  large  difference 
of  temperature  between  the  various  parts  of  the  covering. 
This  disadvantageous  trait  remains  even  though  it  is  con- 
sidered that  the  vertical  electrodes  act  with  a  sort  of  umbrella 
action,  and  in  so  doing  at  least  keep  the  most  intense  heat 
away  from  the  roof.  It  is  to  be  noted  here  that,  for  instance, 
the  roof  of  the  1 5-ton  furnace  at  the  Illinois  Steel  Co.,  has  to  be 
changed  about  every  three  weeks.  According  to  the  Metal- 
lurgical and  Chemical  Engineering,  a  roof  such  as  this  costs  about 
$60  with  silica  brick  costing  $27  per  thousand. 

The  difficulties  of  very  large  diameter,  24-26  inches,  electrodes 
have  not  yet  been  overcome,  as  may  be  judged  from  the  report 
appearing  in  the  Metallurgical  and  Chemical  Engineering,  for 
1910,  p.  i79ff.,  where  the  electrode  temperature,  just  where  it 
issues  from  the  furnace  was  measured  and  gave  1050°  C.  It  is 
evident  that  these  electrode  temperatures  cause  a  greater  con- 
sumption of  the  electrodes,  so  that  this  may  also  be  looked  upon 
as  part  of  the  cause  for  the  consumption  of  6.6  Ib.  (3  Kg.)  of 
graphite  electrodes  per  ton  of  steel  when  charging  hot  metal. 

It  is  also  to  be  noted  that  it  must  be  possible  to  change  the 
slag  in  an  electric  furnace,  as  is  now  done  in  the  open  hearth 
furnaces.  The  removal  of  this  slag,  however,  becomes  more 
difficult  with  the  increase  in  the  size  of  the  furnaces,  because  the 
slag  must  be  entirely  removed.  A  mere  running  off  of  the  slag 
is  not  sufficient,  but  a  thorough  rabbling  off  is  necessary.  In 
taking  these  conditions  into  consideration  the  Electrochemical 
and  Metallurgical  Industry,  of  1909,  p.  262,  says  in  referring 
to  the  attainable  size  of  the  Heroult  furnace: 


146       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

"As  to  the  maximum  size  of  furnace  which  it  is  now  possible 
to  construct,  it  is  the  intention  to  build  them  up  to  30  tons. 
Very  much  will  depend,  however,  on  the  work  which  has  to  be 
accomplished,  that  is  to  say,  whether  one  or  two  slags  would 
be  used.  In  case  of  one  slag,  Mr.  Turnbull  is  sure  that  a  3O-ton 
furnace  is  possible,  but  should  two  slags  be  used,  owing  to  the 
difficulties  which  might  be  encountered  in  raking  off  the  first 
slag  it  may  be  found  that  a  1 5-ton  capacity  is  nearing  the  limit. 
It  could  certainly  be  worked  quicker  than  one  of  a  3O-ton  capa- 
city." 

Attention  is  again  called  here  to  the  influence  of  the  furnace 
size  on  the  thermal  efficiency  of  Heroult  furnaces,  and  this  point 
is  dwelt  upon  more  in  detail.  Prof.  Eichhoff  says  the  following 
in  Stahl  und  Eisen,  1908,  p.  844: 

"I  cannot  think  of  a  small  furnace  that  has  an  efficiency  of 
more  than  50%.  If  the  furnaces  become  larger  and  larger, 
then  the  actual  useful  absorption  of  the  heat  may  rise  to  70%, 
for  the  reason  that  the  furnace  surface  does  not  increase  in  the 
same  ratio  as  the  furnace  contents  do.  As  the  furnaces  become 
larger  the  losses  gradually  decrease,  going  from  50  to  40,  and  from 
30  to  25%.  I  can  tell  you  from  my  own  practical  experience, 
that  comparing  a  3-ton  furnace  to  a  i. 5-ton  furnace,  the  effective 
current  increase  was  only  10%.  Hence,  the  current  consump- 
tion per  ton  of  steel  decreases  materially.  Owing  to  this  fact 
we  are  compelled  to  build  larger  furnaces,  and  there  is  no  reason 
why  this  cannot  be  done." 

Since  then  there  has  been  built  the  furnace  of  25  tons. 
For  this  size  the  above  deductions  are  correct,  however,  with 
the  limitations  that  the  furnace  efficiency  cannot  be  further 
increased  by  further  increasing  the  size  of  the  furnace  unit.  The 
efficiency  of  furnaces  of  increasing  sizes  with  two  electrodes 
follows  the  curve  of  a  parabola.  However,  where  three  elec- 
trodes are  used,  the  efficiency  will  naturally  decrease,  due 
to  the  higher  thermal  losses,  which  latter  gradually  reach  the 
practicable  attainable  minimum,  with  the  increasing  size  of 
furnaces.  As  Heroult  furnaces,  however,  are  built  today,  these 
losses  will  not  be  less  than  25%. 

It  is  difficult  to  calculate  definite  Heroult  furnace  installation 
costs,  as  these  will  in  all  cases  be  determined  largely  by  local 


THE  HEROULT  FURNACE  147 

conditions.  It  is  necessary  to  install  a  low  tension  regulating 
transformer  near  the  furnace,  which  lowers  the  higher  potential 
of  the  central  power  plant.  As  the  Heroult  furnace  therefore 
may  be  connected  to  any  existing  power  line,  it  is  not  necessary 
to  take  into  consideration  the  cost  of  building  a  power  plant  and, 
in  the  United  States,  the  cost  of  installing  a  6-ton,  three-phase 
Heroult  furnace,  with  all  equipment  from  the  connection  with 
the  high  tension  power  line,  is  about  $45,000.  In  the  United 
States  complete  units  of  one  and  two  tons  capacity  are  being 
sold,  ready  to  set  up,  for  $18,000  and  $24,000,  in  all  cases  with 
the  usual  royalty  per  ton  of  metal  poured. 

In  all  the  above  calculations,  the  cost  of  buildings,  etc., 
are  omitted. 

In  closing,  the  advantages  which  Heroult  himself  gave  of 
his  furnace,  over  other  arc  furnaces,  are  here  set  down,  especially 
those  opposed  to  the  Girod  furnace,  which  latter  is  described  in 
the  following  chapter.  The  advantages  mentioned  are  taken 
from  the  Electrochemical  and  Metallurgical  Industry,  for  1909, 
p.  261: 

"First — The  total  absence  of  electrical  parts  in  the  furnace 
proper,  it  being  nothing  else  but  a  modified  open  hearth  with 
the  heat  introduced  above  the  metal  by  the  electric  current  in 
place  of  gas.  This  in  itself  is  an  important  factor  as  it  does 
away  with  the  bottom  pole,  considered  by  Heroult  to  be  always 
the  cause  of  much  trouble  in  electric  furnace  work,  and  allows 
of  any  patching  necessary  to  the  bottom  or  side,  without  inter- 
fering with  the  work  of  the  furnace. 

"Second — The  heat  being  introduced  by  means  of  two 
electrodes  working  in  series,  the  current  passing  through  the 
bath  from  one  electrode  to  another  and  vice  versa,  necessitates 
carrying  only  one-half  the  current  that  would  be  the  case  should 
the  current  flow  from  one  electrode  through  the  bath  and  then 
through  the  bottom  of  the  furnace,  if  the  power  is  the  same  in 
both  cases.  Thus,  all  the  conductors  are  reduced  to  one-half  the 
section  required  in  the  other  case  and  the  electrodes  can  perform 
more  efficient  work  owing  to  the  lesser  density  of  current  to  be 
carried." 

The  above-mentioned  advantages  of  the  Heroult  furnace 
should  be  compared  to  the  advantages  of  the  Girod  furnace, 


148       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

mentioned  at  the  end  of  the  following  diaper.  Furthermore, 
the  opinion  in  the  first  paragraph  may  be  supported.  It  is 
correct,  of  course,  that  certain  advantages  accrue  by  lessening 
the  cross-section  of  the  current  carrying  conductors.  He,  how- 
ever, avoids  mentioning  that  these  advantages  are  only  attainable 
by  raising  the  voltage.  The  opinion  of  Heroult  that  the  series 
connection  of  the  electrodes  gives  more  useful  work,  is  not  sub- 
stantiated in  any  way.  We  shall  see  later  on  that  the  total 
electrode  cross-section  of  the  Heroult  furnace  is  not  greater 
than  with  the  Girod  furnace,  disregarding  entirely  how  incom- 
prehensible it  is  that  Girod  does  not  also  operate  with  the  same 
current  density  and  the  same  low  current  densities  as  Heroult 
does.  It  still  remains  to  be  proved  that  operation  with  low 
current  densities  is  an  advantage,  irrespective  of  the  size  of  the 
furnace.  One  of  the  1 5-ton  furnaces  at  South  Chicago  has  been 
operated  with  1 2-inch  graphitized  carbon  electrodes,  thus  in- 
creasing the  current  density  four  times,  compared  to  some  of 
the  earlier  methods,  when  24-inch  round  carbon  electrodes  were 
used.  Lately  again,  however,  as  large  as  26-inch  diameter 
carbon  electrodes  have  been  used  in  the  20-ton  furnace 

Relative  to  the  use  to  which  the  Heroult  furnace  has  been 
put,  reference  may  be  had  to  the  statistics  in  the  closing  chapter. 
Licenses  for  Heroult  furnaces  may  be  obtained  in  Germany  from 
the  Elektrostahl,  G.  M.  b.  H.,  Remscheid,  Hasten,  and  in  the 
United  States  from  the  United  States  Steel  Corporation,  New 
York. 


CHAPTER  IX 
THE   GIROD   FURNACE 

THE  Girod  furnace,  as  well  as  the  Heroult  furnace,  deserves 
the  greatest  consideration  among  arc  furnaces.  Girod  originally 
made  ferro  alloys  in  a  resistance  furnace,  in  which  the  heat  flow 
went  through  the  walls,  as  described  in  Chapter  III.  It  was  in  1906 
and  1907  that  he  turned  quite  experimentally  to  the  melting  of 
iron.  He  built  a  furnace  with  a  capacity  of  about  i  to  1^2  tons  of 
a  similar  type  to  that  used  by  Heroult,  before  the  latter  went  over 
to  his  electric  furnace  with  series  connected  electrodes.  Where 


FIG.  61. 

Heroult  did  not  succeed  in  obtaining  satisfactory  results  with  his 
furnace,  having  one  pole  in  the  form  of  a  hanging  electrode,  and 
the  other  pole  as  a  bottom  electrode,  Girod  succeeded.  Girod' s 
success  has  been  so  great  in  bringing  this  furnace  to  such  a  fully 
developed  scientific  reality,  that  it  was  hard  to  say  at  first  to 
which  of  these  two  contestants,  in  the  arc  furnace  field,  where 
the  metal  bath  is  used  to  conduct  the  current,  the  victory  in  so  far 
would  finally  belong. 

149 


150     ELECTRIC  FTTRNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

In  outward  appearances  the  Girod  furnace  greatly  resembles 
the  Heroult  furnace.  The  furnace  casing  is  made  of  steel  plate 
and  either  of  the  round  or  rectangular  form.  This  in  turn  re- 
ceives a  lining  of  either  dolomite  or  magnesite,  making  the  bath 
either  round  or  square  shaped,  as  the  case  may  be.  The  furnace 
roof  is  made  of  silica  brick  and  is  removable.  The  furnace  itself 
is  of  the  tilting  variety.  Because  of  this  the  first  furnace  at 
Ugine,  France,  was  provided  with  trunnions  at  the  side,  which 
allowed  the  furnace  to  tilt  in  its  bearings.  In  the  newer  design 
the  furnace  casing  is  furnished  with  a  saddle  resting  in  rollers, 


FIG.  62. 

as  shown  in  Figs.  61  and  62.  The  power  for  the  tilting  mechan- 
ism may  be  of  any  kind,  but  is  usually  an  electric -motor.  The 
Girod  furnaces  are  supplied  with  two  doors,  one  of  which  serves 
mainly  for  the  charging  and  operating  of  the  furnace,  while  the 
other  is  provided  with  a  teeming  spout,  for  the  tapping  of  the 
furnace. 

The  most  interesting  part  of  the  Girod  furnace  is,  of  course, 
the  arrangement  of  the  electrodes  in  which  centres  the  whole 
principle  of  the  furnace.  Where  in  the  Heroult  furnace  the 


TinC    GIROD    FURNACE  151 

electrodes  are  of  opposite  polarity  and  arranged  above  the  bath, 
Girod  avoids  this  by  placing  one  pole  above  and  one  beneath 
the  bath.  When  the  current  strength  increases  with  larger 
furnaces,  and  a  duplication  of  the  electrodes  becomes  neces- 
sary, then  these  are  connected  in  parallel.  This  always  per- 
mits electrodes  of  the  same  size  to  be  used,  and  like  poles  are 
therefore  either  only  above  or  below  the  molten  metal.  This 
arrangement,  which  naturally  only  allows  the  electrode  above 
the  bath  to  be  of  carbon,  from  which  the  current  flows  to 
the  liquid  steel  in  the  form  of  an  arc,  allows  the  other  pole  lying 
beneath  the  bath  to  be  of  a  special  formation.  In  the  Girod 
furnace  this  bottom  electrode  consists  of  a  number  of  soft  iron 
rods,  which  are  arranged  at  the  edges  of  the  hearth,  as  seen  in 
the  horizontal  cross-section  of  Figs.  61  and  62.  In  order  to  avoid 
these  bottom  electrodes  from  melting  off  too  far,  the  parts  pro- 
truding through  the  furnace  bottom  are  water  cooled.  During 
the  operation  then  a  part  of  these  electrodes  melts  away,  after 
which  pasty  layers,  followed  by  solid  ones,  issue  toward  the 
bottom  of  the  electrode  material,  as  soon  as  the  cooling  on  one 
side  is  balanced  by  the  heating  on  the  other.  The  part  of  the 
electrode  which  is  melted  away  is  about  5  to  10  cm.  (2  to  4  inches) 
long,  whereas  the  space  for  the  water-cooling  at  the  lower  end 
of  the  iron  block  is  150  mm.  (6  inches)  deep.  This  water  cooling 
not  only  provides  a  nearly  unlimited  durability  to  the  bottom 
electrodes,  but  it  also  materially  aids  the  life  of  the  bottom 
refractories.  From  data  given  by  Borchers,  the  furnace  bottom 
is  said  to  last  120  to  160  heats  when  melting  cold  stock,  before 
repairs  are  necessary.  During  this  time  the  bottom  wears  away 
to  the  extent  of  100  mm.  (4  inches),  whereas  the  walls  of  the 
furnace  need  repairing  after  only  80  heats. 

It  may  also  be  mentioned  here,  that  Girod  endeavored  to 
utilize  air  cooling  in  place  of  water  cooling  for  the  bottom  elec- 
trode, but  at  present  water  cooling  is  again  generally  used. 

What  has  been  said  of  the  Heroult  furnace  relative  to  the 
hanging  carbon  electrode  also  applies  here.  The  adjustable 
electrodes  are  held  in  their  supports,  which  are  in  turn  fastened 
to  the  furnace.  The  regulation  is  automatic  and  the  Thury 


152      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

regulators  are  used.  Another  similarity  is  to  be  found  in  the 
method  pursued  for  cooling  the  furnace  roof,  where  the  electrodes 
enter  the  furnace. 

The  operation  of  the  furnace  and,  with  it,  the  duration  of 
the  treatment,  is  much  the  same  with  the  Girod  furnace  as  with 
the  Heroult.  This  applies  as  long  as  hot  charges  are  being 
treated,  for  when  it  comes  to  melting  cold  charges,  the  Girod 
furnace  shows  undeniable  advantages  over  the  Heroult  furnace. 
This  is  because  the  vertical  path  of  the  current  does  not  permit 
any  short  circuits  at  almost  full  voltage,  when  the  upper  electrode 
touches  the  top  of  the  scrap  pile.  When  the  electrode  is  lifted 
clear  of  the  furnace,  the  scrap  entirely  fills  its  interior,  and  the 
short  circuits  are  avoided,  as  the  current  path  necessarily  makes 
a  multitude  of  small  arcs  between  the  various  pieces  of  scrap. 
This  equalizes  the  heating  of  the  whole  furnace  content,  thus 
causing  the  whole  charge  of  scrap  to  gradually  collapse  and  melt. 
However,  it  must  not  be  left  unsaid  that  the  above  conditions 
are  present  only  when  the  scrap  is  charged  into  the  furnace  as 
the  best  operating  conditions  of  the  furnace  demand;  that  is, 
the  scrap  is  not  to  be  thrown  in  arbitrarily.  The  most  advan- 
tageous condition  for  melting  cold  stock  is  when  this  is  in  the 
smallest  of  pieces,  and  the  conditions  become  more  disadvan- 
tageous with  the  growing  number  of  larger  pieces.  For  these 
latter  offer  far  too  little  resistance  to  the  current,  if  the  above 
method  were  used  by  starting  with  the  upper  electrode  touching 
the  top  of  the  scrap  pile.  Similarly  it  is  always  necessary  to 
spread  a  layer  of  the  smallest  sized  scrap  on  the  hearth,  so  that 
good  contact  can  be  made  from  the  start  with  the  bottom  elec- 
trode, the  end  of  which  naturally  lies  a  little  low  after  the  furnace 
has  been  in  operation  for  a  while.  In  order  to  make  a  good 
contact  possible  between  the  bottom  electrode  and  the  charge, 
care  must  be  taken  that  no  slag  remains  in  the  indentation 
over  the  iron  electrode,  otherwise  this  cold  slag  would  act  as 
a  conductor  of  the  second  class,  and  in  this  state  act  as  an 
insulator. 

We  now  come  to  the  electrical  conditions  of  the  Girod  furnace. 
Heretofore  this  furnace  has  been  built  mostly  in  two  sizes.     The 


THE    GEROD    FURNACE  153 

smaller  size  of  2>^  tons  capacity  shown  by  Fig.  61  and  the  larger 
size  of  10  and  12  tons  shown  by  Fig.  62.  The  smaller  furnace 
takes  about  $00  Kw.  and  the  larger  from  1000  to  1200  Kw.  As 
the  current  is  only  interrupted  by  one  arc  the  resistance  of  the 
whole  circuit  of  the  Girod  furnace  is  comparatively  small.  From 
this  it  follows  that  a  comparatively  low  voltage  suffices,  in  order 
to  give  the  furnace  its  needed  energy.  The  voltage  therefore 
for  the  300  Kw.  furnace  is  from  60  to  65  volts,  and  with  the  1000 
to  1200  Kw.  furnace  it  is  70  to  75  volts. 

The  single  phase  furnace  has  only  two  poles,  one  above  and 
one  below  the  bath,  naturally  only  single  phase  current  can 
be  used.  As  the  first  Heroult  furnaces  were  operated  almost 
exclusively  from  25  cycle  circuits,  so  the  Girod  furnaces  at  first 
operated  exclusively  from  circuits  of  this  periodicity.  The 
first  trial  furnace  of  i%  tons  tapping  weight  operated  from  a 
35  cycle  circuit,  using  40  to  60  volts,  4000  to  6000  amperes  and 
giving  a  power  factor  of  .65%. 

The  low  voltage  of  the  Girod  furnace  naturally  necessitates 
a  comparatively  large  current,  and  with  it  very  considerable 
cross-sections  in  the  conductors  between  the  furnace  transformer 
and  the  furnace.  This  is  very  noticeable  when  comparing  the 
furnace  with  a  Heroult  furnace  having  an  equal  charging  capacity 
and  the  same  power  input.  It  is  this  lower  voltage  which  makes 
this  part  of  the  installation  more  expensive  than  would  be  the 
case  with  a  furnace  having  a  higher  operating  voltage.  We 
must,  however,  take  into  consideration  that  the  lower  voltage 
also  has  its  advantages.  We  only  mention  the  fact  that  it  is 
easier  to  insulate  this  voltage  from  the  furnace  refrac- 
tories, and  there  is  less  danger  for  those  operating  the 
furnace. 

The  Girod  furnace  now  also  built  polyphase  is  no  longer 
youngest  among  the  better  known  arc  furnaces.  It  has  since 
consequently  been  established  how  best  to  operate  the  furnace. 
There  is,  and  justly  so,  the  recurrent  opinion  that  the  Girod 
furnace  is  radically  different  from  the  Heroult,  owing  to  the 
fact  that  the  bath  is  connected  in  the  circuit  in  a  different  way. 
We  have  already  alluded  to  the  advantage  of  the  current 


154      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

passing  through  the  steel  and  iron  in  a  vertical  direction,  when 
melting  cold  scrap.  We  desire,  however,  to  discuss  the  operation 
of  the  furnace  when  the  charge  is  melted. 

As  we  have  seen,  the  current  passes  through  the  bath  in 
a  horizontal  direction,  in  the  Heroult  furnace,  and  in  a  vertical 
direction  in  the  Girod  furnace.  With  the  Heroult  furnace, 
however,  mention  is  never  made  of  any  essential  influence  of  the 
purely  resistance  heating,  which  occurs  because  the  current  must 
overcome  the  resistance  of  the  bath,  yet  with  the  Girod  furnace 
we  often  find  an  important  heating  effect  ascribed  to  it.  In  order 
that  there  shall  be  no  misunderstand'ng,  it  may  be  said  that  the 
different  manner  in  which  the  current  goes  through  the  bath  in 
both  furnaces  causes  different  effects,  yet  these  effects  do  not 
cause  a  greater  or  less  resistance  heating,  (caused  by  the  current 
passing  through  the  bath,)  but  rather  a  difference  in  the  circula- 
tion phenomenon.  This  may  be  decidedly  more  advantageous 
in  one  case  than  in  another.  To  which  misleading  points  of 
view  our  opinions  lead  us  to  suppose  that  the  resistance  heating, 
(even  with  a  molten  bath,)  is  of  considerable  influence,  is 
shown  in  a  short  article  on  the  Girod  furnace  in  Stahl  und 
Eisen,  for  1908.  Here  it  is  pointed  out  that  the  depth  of  the 
melted  iron  of  the  Girod  furnace  may  easily  be  increased  from 
30  cm.  (12  inches),  to  75  cm.  (30  inches),  or  more.  With  all  this 
the  pure  resistance  heating  is  supposed  to  heat  the  whole  bath 
evenly  throughout  its  total  depth.  In  spite  of  this,  though, 
Girod  with  his  10-  to  1 2-ton  furnaces  only  used  a  depth  of  bath 
equal  to  30  cm.  (12  inches). 

A  large  surface  bath  has  much  greater  radiation  losses  as  a 
consequence  than  a  bath  has,  having  great  depth  and  a  lesser 
surface.  The  above  example  of  the  1 2-ton  furnace  really  proves 
that  the  resistance  heating  in  a  Girod  furnace  can  be  entirely 
ignored,  as  soon  as  the  furnace  content  is  molten.  We  can  also 
convince  ourselves  of  this  arithmetically. 

If  we  take,  for  example,  the  2>^-ton  Girod  furnace,  we  find 
by  consulting  Fig.  61,  that  with  a  depth  of  bath  equal  to  240  mm. 
(9.1  inches),  the  average  bath  cross-section  is  about  1200  X  1200 
sq.  mm.  (48  X  48  sq.  inches).  If  we  take  the  specific  resistance 


THE    GIROD    FURNACE  155 

of  the  bath  at  1.66,  as  given  on  page  15,  we  find  the  ohmic  resist- 
ance of  the  bath, 

=  P  X        =  1.66  X  4  -  -»8  X  .or*  ohm. 


A  furnace  of  this  kind  takes  about  300  Kw.  at  60  volts. 
With  a  power  factor  of  .8%  it  gives  a  current  of 
300,000 

6o~^T  =  625°  amperes' 

The  energy,  therefore,  transformed  in  the  bath  is: 
i2  X  r  =  6250"  X  .28  X  io-6  =  10.94  watts. 

This  amount  is  only  —    —  of  i%  of  the  300,000  watts  delivered 

to  the  furnace,  and  everybody  must  admit  that  any  such  small 
amount  of  energy  has  absolutely  no  effect  on  the  heating.  If, 
on  the  other  hand,  we  figure  the  current  density  in  the  bath,  we 
will  see  that  this  comparison  also  shows  the  heating  of  the  molten 
metal  to  be  entirely  uninfluenced  by  the  current  flowing  through 
this  resistance,  and  that  the  resistance  heating  of  the  carbon 
electrodes  is  much  more  important  than  the  resistance  heating  in 

the  bath.     The  example  we  have  before  us  gives.  -  —  = 

'  1200  X  1200 

6250 

-°°44   ampereS  Per  SqUare  milhmetre 


6  2  co       2.71  amperes  per  )     , 

—  =  -i        r  which   allots  210  sq.   millimetres  to 

2304  square  inch      ) 

i  ampere  (about  .36  sq.  in.  per  ampere).  If  we  compare  this 
with  the  current  density  in  the  carbon  electrode,  which  con- 
ducts the  same  current  that  flows  through  the  bath,  and  has 
a  cross-section  corresponding  to  a  diameter  of  350  mm.  or 
96211  sq.  mm.  (13^  inches  dia.  gives  149  sq.  inches)  with  the 
300  Kw.  furnace,  we  observe  that  we  only  obtain  a  cross-section 

,06211  /  149       .024  square  in.  \ 

per    ampere  of  ~,  --  =  15.4  sq.  mm.  I—  —  = 

6250  ^6250      per  ampere.    / 

With  all  this  it  is  well  to  note  that  the  comparison  of 
these  absolute  values  gives  a  much  too  favorable  picture,  because 
no  consideration  has  been  taken  of  the  higher  specific  resistance 
of  the  carbon  compared  to  the  iron  bath.  In  accordance  with 


156  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

data  on  page  15,  we  figured  the  specific  resistance  of  fluid  iron 
as  p  =  1.66.  This  resistance  refers  to  a  length  of  i  m.  (39.37 
inches),  and  i  sq.  mm.  (.0155  sq.  inch),  cross-section.  With 
electrodes  in  the  operating  condition  we  figured  p  '=  .0056  (see 
page  130).  This  value  corresponds  to  a  length  of  i  cm.  (.4  inch), 
at  a  cross-section  of  i  sq.  cm.  (.155  sq.  inches).  If  we  convert 
this  value  to  one  corresponding  to  a  length  of  i  m.  (39.37  inches), 
with  a  cross-section  of  i  sq.  mm.  (.0155  sq.  inches),  we  acquire 
the  value  for  carbon  in  the  operating  condition,  when  p  =  56. 

That  is   to  say,  the  specific  resistance  of  the  carbon  is  — — 

I  .OO 

or  say,  35  times  larger  than  that  for  iron.  From  this  it  follows 
that  even  with  equal  lengths  and  cross-sections,  35  times  as  much 
energy  is  transformed  into  heat  in  the  carbon  as  in  the  iron  bath. 
It  is  obvious  that  the  carbon  has  a  much  smaller  cross-section 
and  a  much  greater  length  than  the  metal  has,  evincing  that  the 
consequent  heat  distribution  is  much  more  unfavorable  for  the 
iron,  when  considering  only  the  resistance  heating.  The  true 
ratio  is  therefore  not  apparent  by  the  above  partial  calculation. 

We  will  now  consider  the  comparison  of  this  furnace  with 
the  ideal  furnace.  We  first  come  to  the  availability  of  any  kind 
of  alternating  current  and  refer  again  to  the  former  remarks,  that 
now  besides  single  phase  current,  three  phase  is  also  available  for 
this  type  of  furnace,  as  the  use  of  three  phase  current  no  longer 
comes  in  conflict  with  the  principle  underlying  the  furnace  design. 
Alternating  current  is  usually  generated  at  a  commensurately 
high  voltage,  brought  to  the  vicinity  of  the  furnace,  and  there 
transformed  into  a  stationary  transformer  to  the  wished-for  low 
tension  current  for  the  furnace. 

It  is  just  as  difficult  to  entirely  avoid  the  power  fluctuations 
with  a  Girod  furnace  as  it  is  with  a  Heroult  furnace;  yet  it  is  to 
be  observed  that  with  the  Girod  furnace  the  current  fluctuations 
in  actual  practise  are  neither  as  violent  nor  do  they  occur  as 
often  as  they  do  in  the  Heroult  furnace.  In  spite  of  the  current 
fluctuations  being  smaller,  they  are  yet  important  enough  in  a 
2^2-ton  Girod  furnace,  which  takes  400  Kw.  on  an  average  with 
a  power  factor  of  .80%,  to  recommend  that  a  50x3  to  550  Kw. 


THE    GIROD    FURNACE  157 

machine  be  employed.  This  example  may  properly  show  why 
the  im'tial  cost  rises  which  really  becomes  noticeable  here,  all 
due  to  these  power  fluctuations.  Finally,  we  may  again  mention, 
that  the  automatic  regulation  is  accomplished  by  means  of 
Thury  regulators.  With  Girod  furnaces,  these  regulators  are  set 
to  keep  the  current  constant,  and  they  in  turn  give  the  electrodes 
their  proper  setting.  . 

The  easy  regulation  of  the  incoming  energy  in  the  Girod 
furnace  is  the  same  as  with  all  other  electric  furnaces. 

The  electrical  efficiency  of  the  furnace  is  influenced,  first  by 
the  probable  installation  of  a  rotary  transformer,  or  by  the 
losses  of  the  stationary  transformer,  (neglecting  the  losses  in 
the  conductors,)  and  finally  by  the  losses  at  the  furnace,  due 
to  the  electrodes.  For  a  general  calculation  we  can  use  the 
following  values: 

Efficiency  of  the  rotary  transformer 85% 

Efficiency  of  the  stationary  transformer 96%  to  97% 

Efficiency  of  the  carbon  electrodes  including  the  heat 

conduction  losses 90% 

All  Girod  furnaces  are  made  of  the  tilting  variety.  The 
hearth  is  easily  surveyed,  and  perfectly  accessible  for  all  operating 
conditions. 

We  now  come  to  the  circulation  of  the  melted  metal  and  once 
more  to  the  fact  that  the  peculiar  path  of  the  current  in  a  Girod 
furnace  is  of  added  importance.  This  circulation  begins  with 
one  or  more  current  centres  above  the  bath,  and  goes  to  the 
bottom  electrodes  set  around  the  periphery  of  the  furnace.  Figs. 
63  and  64  show  the  diagrammatic  connections  for  the  current 
paths  in  a  Girod  furnace,  Fig.  63  being  the  plan  view  and  Fig.  64 
showing  the  cross-section  at  a  c.  The  dots  and  crosses  indicate 
the  lines  of  force,  which  follow  the  arrows  according  to  the  laws 
given  in  Chapter  III.  As  lines  of  force  of  the  same  direction 
repel  while  those  of  opposite  direction  attract,  and  as  the  molten 
bath  in  a  certain  sense  can  be  regarded  as  a  movable  conductor, 
with  the  vertical  electrodes  over  and  under  the  bath  considered 
as  fixed  conductors,  we  find  in  the  molten  steel  certain  circulation 
phenomena,  as  shown  by  the  arrows  in  Fig.  64.  That  is  to  say, 


158      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


a  definite  circulation  will  appear  throughout  the  entire  bath,  of 
such  a  nature,  that  a  current  of  metal  can  be  observed  going 
from  the  walls  of  the  furnace  toward  the  centre,  from  there  to 
the  bottom,  and  back  again  to  the  walls.  The  strength  of  this 
circulation  phenomenon  depends  on  one  hand  on  the  strength  of 
the  current  which  flows  through  the  bath  that  is  then  collected 
at  the  electrodes,  and,  on  the  other  hand,  on  the  depth  of  the 


FIG.  63. 


FIG.  64. 


bath.  For  it  is  evident  that  the  circulation  in  the  bath  would 
instantly  cease  if  the  metal  currents  were  in  a  vertical  direction, 
instead  of  being  in  an  almost  horizontal  direction.  If  the  bath 
has  a  comparatively  great  depth,  we  would  approach  the  vertical 
direction  condition.  We  ascertained  before,  that  as  the  heating 
in  a  Girod  furnace  is  practically  entirely  from  the  arc,  a  great 
depth  of  bath  is  therefore  precluded,  so  we  see  now  that  the 
advantageous  mixing  in  the  bath  would  cease  if  this  were,  say, 
over  40  cm.  deep  (about  16  inches),  this  adequate  mixing  being 
present  with  shallow  baths  or  those  of  normal  depth.  With  poly- 
phase furnaces  one  or  two  phases  are  purposely  unbalanced  so 
that  an  appreciable  amount  of  current  will  flow  through  the 
neutral  or  centre  point  of  a  star  connection,  which  goes  to  the 
bottom  electrodes,  thus  adding  to  the  circulation. 

The  application  of  the  Girod  furnace  for  the  steel  industry 
is  one  of  the  widest.  It  has  already  been  said  that  very  good  re- 
sults are  obtained  with  furnaces  of  the  1 2-ton  size.  Here,  however, 
they  already  use  four  electrodes  of  considerable  cross-sections. 

There  is  then  no  reason  why  Girod  furnaces  cannot  be  built 
of  the  same  capacities,  as,  for  instance,  the  Heroult  furnaces. 


THE   GIROD   FURNACE  159 

even  though  the  Girod  furnaces  operate  with  a  lower  voltage  than 
the  Heroult  furnaces,  and  both  now  operate  with  three  phase 
current.  If  the  Girod  only  used  single  phase  current  we  will 
assume  having  1200  Kw.  energy  at  .80%  power  factor,  to  be 
used  by  means  of  three  phase  current  at  no  volts  on  the  one 
hand  and  at  single  phase  current  at  70  volts  on  the  other,  in  the 
former  case  for  a  Heroult  and  the  latter  case  for  a  Girod  furnace. 
Then,  per  phase,  we  obtain  for  the  three  phase  Heroult 
furnace,  a  current  of 

1200000 

^h  =  —  —  =  7882  amperes, 

no  X  1.73  X  .8 

and  for  the  single  phase  Girod  furnace  the  current: 

'.  1 2OOOOO 

tg  =  —         -  =  21429  amperes. 
70  X  .8 

Now  Heroult  has  to  deal  with  7882  amperes  for  each  phase, 
i.e.,  three  electrodes  are  needed  each  to  carry  7882  amperes, 
whereas  Girod  has  only  once  to  carry  a  current  of  21429  amperes. 
Suppose  we  assume  that  he  too  uses  three  electrodes,  connected 
in  parallel  of  course,  then  each  would  carry  a  current  equal  to 
21429  -f-  3  =  7143  amperes.  In  other  words,  it  would  even 
suffice  Girod  to  have  a  lesser  total  electrode  cross-section  than 
Heroult,  though  the  latter  has  a  much  higher  current  in  the 
electrodes  at  the  same  current  density.  Or  we  may  say:  "The 
influence  of  carrying  the  current  in,  one  way  or  another,  is  of  so 
little  importance  as  regards  its  effect  on  the  carbon  electrodes, 
and  that  the  electrode  relation  in  both  types  of  furnaces  may  be 
regarded  as  being  exactly  alike."  Therefore,  the  same  reasons 
governing  the  maximum  size  of  the  Heroult  furnace  cover  the 
Girod  furnace  also,  so  that  the  attainable  size  of  either  furnace 
is  on  the  same  footing.  No  limitation  of  the  applicability  of  the 
Girod  furnace  any  longer  arises  as  the  furnace  is  now  also  built 
for  polyphase  current,  which  precludes  expensive  rotary  trans- 
former units  for  large  furnaces,  and  enables  current  of  an 
existing  three  phase  central  station  to  be  used.  If  no  con- 
sideration need  be  taken  of  an  existing  power  plant,  even  then 
the  single  phase  generators  for  large  Girod  furnaces  will  be  more 


160     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

expensive  than  three  phase  machines  of  the  same  size  for  Heroult 
furnaces.  Regarding  the  uninfluencing  e/ect  of  the  electric  heating 
on  the  chemical  composition  of  the  bath  the  comment  given  on 
page  140  is  also  applicable  here.  This  applies  to  all  arc  furnaces 
which  have  their  electrodes  directed  directly  against  the  metal 
to  be  treated. 

Especially  worthy  of  mention  with  the  Girod  furnace  is  the 
influence  which  the  water-cooled  bottom  electrode  exercises, 
even  though  this  influence  is  said  to  be  of  no  consequence.  To 
understand  this,  consider  that  the  circular  motion  in  the  bath 
also  continually  renews  the  coldest  material  over  the  bottom 
electrode,  so  that  in  spite  of  the  greater  temperature  difference 
between  the  bath  surface  and  hearth  bottom,  there  remain  prac- 
tically the  same  conditions  as  in  the  Heroult  furnace. 

In  coming  now  to  the  consummate  efficiency  of  the  Girod 
furnace,  it  may  be  again  said  that,  compared  to  the  Heroult 
furnace,  the  proportions  of  the  carbon  electrodes  in  both  furnaces 
may  be  looked  upon  as  being  equal  to  each  other.  From  this 
it  follows  that  not  only  are  the  electrical  losses  equally  great, 
but  the  thermal  losses  also,  for  these  are  caused  by  the  hanging 
carbon  electrodes.  Also,  the  water-cooling  losses,  caused  by 
the  devices  at  the  roof  of  the  furnace,  where  the  carbon  electrodes 
pierce  it,  are  by  no  means  unimportant.  According  to  the  report 
of  Conssergues  these  are  about  10%;  for  it  was  established  that 
the  power  consumption  with  the  Girod  furnace  decreased  10% 
when  it  was  operated  without  the  water  cooling.  The  fact  that 
water  cooling  apparatus  is  used  today  on  all  Girod  furnaces  as 
well  as  on  nearly  all  other  arc  furnaces,  may  be  explained  by  the 
following  reasons,  (as  discussed  on  page  100,)  first,  a  tighter  fit 
can  be  made  at  the  water  cooling  entrance  to  the  furnace,  the 
electrodes  being  better  protected  against  oxidation,  and,  secondly, 
because  the  water-cooled  boxes  allow  the  furnace  roofs  to  be 
stiffened,'  which  latter  have  their  life  considerably  prolonged. 
Besides  these  roof  and  wall  radiation  losses  of  the  furnace  which 
are  about  equal  in  the  Girod  and  Heroult  furnaces,  there  remain 
still  to  the  detriment  of  the  Girod  furnace  the  losses  of  the  water- 
cooled  bottom  electrode.  These  are  avoided  in  the  Heroult 


THE   GIROD   FURNACE  161 

furnace.1  We  come  to  the  conclusion,  therefore,  that  the  losses 
due  to  the  cooling  of  the  bottom  electrode  are — according  to 
an  address  by  Trasensters — "much  less  important,"  than  those 
which  are  occasioned  by  the  cooling  where  the  roof  is  pierced 
for  the  carbon  electrodes. 

In  order  to  further  judge  the  total  efficiency  of  the  Girod 
furnace,  the  following  notation  is  taken  from  a  report  of  the 
firm,  Ohler  &  Co.,  of  Aarau,  in  Switzerland.  (See  Electro- 
chemical and  Metallurgical  Industry,  1908,  pp.  452  and  453.) 
Here  we  first  find  a  description  of  Girod  furnace  installation  at 
the  above  works.  The  furnace  is  connected  to  the  power  of 
the  municipal  power  plant,  through  the  medium  of  a  motor- 
generator  set.  The  2000  volt,  2  phase  current  system  supplies 
the  Ohler  Works'  motor  of  450  HP,  running  at  560  R.P.M., 
and  is  coupled  directly  to  a  single-phase  alternator  giving  4600 
to  5000  amperes  at  65  to  75  volts  and  a  frequency  of  37.4  periods 
per  second.  Twelve  heavy  copper  cables,  each  20  mm.  in 
diameter  and  composed  of  12  copper  wires  twisted  together, 
carry  the  current  10  metres  to  the  furnace.  The  voltage  drop 
is  2.5  volts  from  the  machine  to  furnace,  so  that  this  short  cable 
installation  alone  causes  a  loss  of  3  to  4%.  At  the  end  of  this 
report  we  find  this  statement.  It  is  calculated  that  the  elec- 
trical part  of  the  plant  has  an  efficiency  of  75  to  80%;  i.e.,  75 
to  80%  of  the  energy  of  the  primary  current  appears  as  heat 
in  the  furnace.  A  rather  approximate  estimate  of  the  calorific 
efficiency  of  the  furnace  itself  shows  about  50%  of  the  current 
converted  into  >  useful  heat. 

Naturally  the  efficiency  with  the  Girod  furnaces  also  rises 
as  the  furnace  increases  in  size.  Yet,  it  is  to  be  noted  that,  when 

1  With  the  same  construction  of  the  Girod  furnace  as  the  Heroult,  other 
things  being  equal,  the  efficiency  of  the  Girod  furnace  must  be  just  that  amount 
less,  which  corresponds  to  the  water  cooling  of  the  bottom  electrode.  Accord- 
ing to  Stahl  u.  Risen,  July  20,  191 1,  by  A.  Miiller,  in  a  3-ton  Girod  furnace,  a 
calorimetric  determination  of  the  heat  carried  out  in  the  cooling  water  of  these 
bottom  electrodes  gave  10.1  kilowatt-hours  for  the  130  minute  run  and  about 
l.oi  per  cent.,  or  2.9  kilowatt-hours  per  ton  of  steel  produced.  The  cooling 
water  used  in  the  top  electrode  carried  out  36.7  Kw.  hrs.,  3.65%  of  total 
energy  supplied  or  10.5  kilowatt-hours  per  ton  of  steel. 


162      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  number  of  the  upper  electrodes  is  increased,  the  efficiency 
curve  decreases  here  as  well.  The  reasons  underlying  this  were 
given  in  the  preceding  chapter  on  the  Heroult  furnace. 

The  costs  of  a  2>£-ton  Girod  furnace,  including  the  electrode 
regulators,  the  switchboard  instruments,  the  tilting  mechanism, 
its  motor  and  short  conductors  between  the  furnace  and  its 
transformer  or  the  dynamo  room,  total  about  $15,000.  A  large 
furnace  of  10  to  12^  tons  with  the  same  equipment  will  cost 
about  $30,000.  To  this  must  be  added  the  transformers  and  the 
royalty  charges. 

The  cost  of  a  complete  Girod  furnace  installation,  but  ex- 
clusive of  the  transformer  or  generator,  and  consisting  of  an 
operating  and  a  reserve  furnace  each  of  2  tons  capacity,  together 
with  the  necessary  equipment  for  pouring  the  steel,  and  the 
accompanying  buildings,  total,  according  to  Borchers,  about 
$40,000  to  $60,000.  An  installation  with  a  10-  to  12^- ton 
furnace  and  a  reserve  furnace  of  the  same  size  will  cost  about 
$60,000  to  $80,000. 

The  power  consumption  with  the  Girod  furnace  is  about  the 
same  as  that  given  for  the  Heroult  furnace.  What  differences 
there  may  be  due  to  a  more  or  less  favorable  efficiency  can  be 
omitted  when  making  arithmetical  calculations,  as  the  power 
consumption  figures  depend  largely  on  the  efficiency  of  the 
furnace,  the  electric  power  at  the  terminals,  as  well  as  on  the 
charge  and  the  final  product.  The  composition  of  the  final 
product  produces  much  greater  variations  in  the  power  con- 
sumption, than  the  differences  in  the  efficiency.  -This,  of  course, 
does  not  hinder  the  furnace  with  the  better  efficiency  to  operate 
with  less  power  and  consequently  with  lower  current  costs, 
provided  that  an  equal  start  is  made  with  like  raw  materials,  and 
like  final  products  achieved. 

The  electrode  consumption  with  the  Girod  furnace  may  be 
taken  to  be  the  same  as  with  the  Heroult  furnace,  for  there  is 
no  reason  why  the  electrode  consumption  should  be  less  with 
one  furnace  than  with  the  other,  when  about  the  same  electrode 
cross-sections  are  used  in  either  case.  Should  there  be  given, 
nevertheless,  larger  or  smaller  values  for  the  consumption 


THE   GIROD   FURNACE 


103 


FIG.  65. 


164      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

figures,  in  one  case  or  another,  the  larger  wear  can,  in  no  case, 
be  based  on  the  principle  of  the  furnace.  Consequently  if  one 
furnace  is  to  have  any  advantage  over  the  other,  it  must  depend 
on  its  more  or  less  successfully  constructed  details. 

In  order  to  give  the  reader  an  idea  what  these  furnaces  look 
like,  Fig.  65  is  shown.  This  pictures  a  5-ton  polyphase  Girod 
at  a  German  Steel  Works.  The  three  electrodes  can  be  plainly 
seen. 

As  the  preceding  chapter  on  the  Heroult  furnace  was  closed 
with  Heroult's  own  opinion  of  the  advantages  of  his  furnace,  so 
this  chapter  is  closed  with  the  deduction  of  Borchers,  where 
he  proves  the  superiority  of  the  Girod  furnace  over  the  Heroult 
furnace.  The  quotation  is  taken  from  Stahl  und  Risen, 
1909,  page  1947,  where  Borchers  says:  "I  strictly  maintain 
that  today  there  is  no  electric  furnace  for  the  refining  of  metal 
which  excels  the  Girod  furnace.  I  make  special  reference  to  the 
uniformity  of  the  current  distribution;  the  uniformity  of  the 
heat  generation  in  the  bath;  the  low  voltage  between  poles,  the 
consequent  lesser  insulation  difficulties;  followed  by  the  con- 
sequent lesser  danger  to  the  operatives;  on  account  of  these 
circumstances,  it  excels  in  its  simplicity  of  construction  as  a 
whole,  and  in  its  operation." 

It  is  well  to  compare  this  with  the  opinion  of  Heroult  given 
on  page  142.  Lastly  we  may  add  that,  if  we  consider  only  the 
evenness  of  the  current  distribution,  and  the  heat  generation  as 
above  mentioned,  these  alone  should  be  enough  to  decide  the 
question.  That  there  is  an  advantage  in  the  lower  voltage  goes 
without  saying.  To  these  we  might  add  the  further  advantages 
of  the  smaller  current  fluctuations,  especially  when  melting  down 
cold  stock,  while  the  opinion  regarding  the  greater  simplicity  and 
the  greater  safety  during  the  operation  of  one  furnace  over  the 
other,  may  be  left  to  the  reader.  Regarding  the  application  of 
the  Girod  furnace,  reference  is  had  to  the  statistics  in  the 
closing  chapter.  Licenses  for  Girod  furnaces  may  be  had  from 
the  inventor,  Paul  Girod,  Ugine,  Savoy,  France,  or  from  his 
American  representative,  C.  W.  Leavitt,  New  York. 


CHAPTER  X 


THE   RENNERFELT  FURNACE 

IN  1878  Siemens  experimented  with  a  radiating  arc  furnace 
having  two  horizontal  electrodes  as  shown  by  Fig.  5.  Twenty 
years  later  Stassano  tried  out  his  first  radiating  arc  furnace, 
single  or  polyphase,  with  electrodes  rigidly  horizontal  or  nearly 
so  in  a  vertical  plane.  This  was  the  first  practical  application 
of  Siemens'  idea  for  electric  furnaces  in  the  iron  and  steel  in- 
dustry. Both  of  these  applications  allowed  the  flame  to  remain 


•Y*E- 


FIG.  650. 

above  the  bath  without  giving  it  any  particular  direction  toward 
the  steel  to  be  melted  or  treated. 

In  1912  Rennerfelt  brought  out  his  directionalized  radiating 
arc  as  shown  by  Fig.  650.  This  shows  two  horizontal  electrodes 
and  one  vertical  coming  together  at  a  point  to  make  the  arc, — 
the  larger  amount  of  current  coming  from  the  top  electrode  and 

165 


166      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


FlG.  656. 


forcing  the  arc  flame  violently  toward  the  bath.  Rennerfelt 
was  granted  patents  covering  this,  the  first  United  States  patent, 
dated  October  23,  1913,  No.  1076518,  etc.  In  the  improved 
form  the  side  electrodes  can  be  tilted  in  a  vertical  plane,  as  shown 
in  the  original  patent  drawing,  and  better  by  Fig.  6$b.1  All  three 
electrodes  are  lowered  as  the  charge  melts,  and  when  molten 
the  best  height  is  chosen  for  the 
flame  to  be  above  the  slag  covered 
charge.  It  is  notable  that  the 
material  being  treated  does  not 
conduct  the  electricity  in  any  way. 
Before  describing  further  details 
of  this  furnace,  we  mention  briefly 
an  account  of  its  development.  In 
1912,  the- Bultfabriken  in  Halsta- 
hammer,  Sweden,  started  the  first 
commercial  furnace  of  this  design, 
since  which  time  over  one  hundred  have  been  placed  in 
operation,  due  to  a  simple  form  of  furnace,  easily  responding 
to  the  metallurgical  demands  made  upon  it. 

Regarding  the  furnace  itself,  this  resembles  a  tilting  open 
hearth,  much  as  the  Heroult  furnace  does.  Perhaps  the  main 
resemblance  between  all  three  being  the  fact  that  these  are  the 
main  electric  furnaces  of  the  arc  type,  except  the  Stassano,  hav- 
ing a  solid  bottom  like  an  open  hearth.  It  consists  today  of  a 
cylindrical  steel  plate  shell,  with  the  horizontal  electrodes  pierc- 
ing the  rounded  walls,  in  all  sizes  up  to  three  tons  holding 
capacity.  The  furnace  hangs  in  trunnions  and  tilts  by  means 
of  an  electric  motor.  The  whole  design  is  shown  plainly  on 
Figs.  656  and  650.  The  bottom  and  sides  are  made  in  much  the 
same  way  as  in  other  furnaces,  and  the  roof  is  removable.  The 
hearth,  being  round  and  having  one  or  two  doors,  is  readily 
inspected  and  easily  surveyed.  The  roof  is  slightly  arched, 
having  a  rise  of  six  or  nine  inches  (15  to  22.5  mm.)  and  is  dome- 
shaped.  With  this  size  furnace  only  a  single  electrode,  prefer- 
ably of  Acheson  graphite,  pierces  the  roof. 

The  furnace  may  be  easily  charged  through  the  doors,  as 

JSeeA.  E.  S.     Vol.  XXXI  —  1917  —  "  Rennerfelt  Electric  Furnace  Oper- 
ation,"  by  C.  H.  Vom  Baur. 


THE   RENNERFELT  FURNACE 


167 


the  electrodes  are  withdrawn  meanwhile.  Where  the  electrodes 
pierce  the  furnace  refractories,  copper  or  iron  cooling  chambers 
keep  the  electrodes  outside  the  furnace  and  brickwork  reasonably 
cool.  Copper  water-cooled  clamps  are  also  necessary  to  fasten 
the  conductors  to  the  electrodes.  The  electrodes  are  fed  by 
means  of  worm  gearing,  and  are  either  hand  controlled,  with 
push-buttons  and  electric  motors,  or  with  electric  motors 
and  regulators  automatically.  With  hand  control  the  arc 
is  usually  steady,  as  shown  by  the  curves  of  Fig.  65^.  That 


FIG.  650. 

is  why,  so  far,  only  four  furnaces  have  been  equipped  with 
either  push-button  or  automatic  electric  control.  With  hand 
regulation  the  side  electrodes  oftentimes  do  not  have  to 
be  touched  for  several  minutes  and  the  top  electrode  once  in 
ten  or  fifteen  minutes. 

Either  hot  or  cold  charges  can  be  treated,  and,  owing  to  the 
inherent  characteristics  of  the  arc,  tending  toward  stability  as 
it  does,  no  heavy  fluctuations  occur.  During  the  melting  period 
choke  coils  are  sometimes  placed  in  series  with  the  current 
entering  the  side  electrodes  which  give  ten,  twenty  or  thirty  volts 
reactance.  These  reduce  the  power  factor  with  sixty-cycle 
current  from  95  to  80%.  With  cold  charges  no  more  fluctuations 
occur  than  when  treating  hot  metal,  because  the  steel,  being 
melted,  be  it  in  small  or  large  pieces,  does  not  affect  the  arc 
flame  in  any  way,  as  the  flame  is  made  independent  of  the  arc, 


168      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

i.e.,  the  continuity  of  the  electricity  is  made  as  easily  with  an 
empty  furnace  as  with  a  full  one.  This  feature  is  sometimes 
called  upon  to  heat  the  bottom  after  the  furnace  has  been  stand- 
ing idle,  and  is  the  means  of  avoiding  skulls  on  the  bottom, 
so  annoying  to  the  steel  maker. 
Fig.  6$d  shows  a  photographic  re- 
production of  the  arc  flame. 

The  steel  bath  is  always  covered 
with  a  suitable  slag.  With  the 
Rennerfelt  furnace  the  entire  heat 
comes  from  above,  as  in  an  open- 
hearth  furnace. 

Electrically  the    furnace  design 
FIG.  65d.  is  sucn  tnat  anY  frequency  can  be 

used  to  advantage  and  still  main- 
tain a  power  factor  of  90%.  So  far,  all  of  these  furnaces 
operate  from  polyphase  circuits.  If  three  phase  is  supplied 
from  the  power  house  it  is  changed  by  means  of  the  Scott 
connection  to  two  phase.  The  prevaih'ng  voltages  at  the  arc 
are  120,  no,  100,  and  80.  A  three-ton  furnace  with  750  KVA 
in  transformers  (two  of  375  KVA  each),  at  100  volts,  gives 
3750  amperes  at  each  side  electrode,  and  5287  in  the  top  elec- 
trode. Care  must  be  taken  while  operating  to  see  that  the  top 
electrode  is  lowered  properly,  otherwise  it  will  not  draw  its 
quota  of  current.  The  side  electrodes  may  be  controlled  by 
automatic  means,  without  any  electrical  complications,  but  to 
attempt  to  regulate  all  three  automatically  and  meet  all  emer- 
gencies causes  serious  complications. 
A  three-ton  furnace  takes 

3750  amperes  X  100  volts  X  2  =  750  KVA, 
and  with  its  90%  power  factor, 

.90  X  750  =  675  Kw. 

Acheson  graphite  electrodes  are  used  usually,  and  in  this  case 
those  of  5^  in.  and  6  in.  diameter  give  good  operating  results, 
especially  when  having  the  new  cone  joint.  This  gives  3.5  sq. 


THE  RENNERFELT  FURNACE  IfiO 

mm.  per  ampere  (182  amperes  per  sq.  in.)  for  each  side  electrode 
and  about  2%  greater  density  for  the  top  electrode.  The  over- 
hanging portion  of  the  side  electrode  is  one  meter  (39^  in.) 
and  the  length  from  the  electrode  clamp  to  the  arc  itself  is 
1.66  meters  (60  ins.).  With  the  specific  resistance  of  graphite 
in  an  operative  condition  taken  at  .00085  °hms  per  cm.  cube, 
the  voltage  drop  is 

e  =  i  X  PI  X  j  =  3750  X  .00085  X  ^, 

where  /  and  q  are  respectively  in  centimeters  and  square 
centimeters,  equals  2.86  volts  per  side  electrode.  The  voltage 
drop  in  the  top  electrode  is  about  the  same,  giving  for  the  three 
electrodes,  say,  8.50  volts  drop.  From  this  it  is  evident  that  to 
raise  the  arc  voltage  from  90  to  120,  decreases  the  electrical 
electrode  losses  from  10  to  7%.  Acheson  graphite,  not  being 
quite  as  strong  as  amorphous  carbon  electrodes  (ratio  8  to  10), 
more  care  must  be  taken  in  handling  them  to  avoid  breakages 
at  the  joints. 

The  power  consumption  varies  not  so  much  with  the  size  of 
the  furnace  as  formerly,  but  today  more  with  the  amount  of 
electrical  heat  behind  the  furnace.  In  1912,  175  to  200  Kw. 
for  a  i -ton  furnace  was  considered  ample.  Five  years  later 
we  find  400  Kw.  in  transformers  behind  a  furnace  of  this  size. 
Naturally  the  time  for  a  heat  is  materially  decreased.  With 
a  basic  bottom  melting  cold  charges  and  taking  off  one  slag, 
heats  of  good  steel  are  regularly  taken  off,  in  less  than  three  hours, 
when  operating  continuously  with  a  consumption  of  670-720 
Kw.hr./ton.  With  an  acid  bottom,  600  to  625  Kw.hr./tonMs 
common  practice  with  an  experienced  and  careful  attendant, 
making  a  steel  suitable  for  castings. 

Coming  now  to  the  comparison  between  the  Rennerfelt 
furnace  and  the  ideal  furnace,  the  first  requirement,  namely, 
that  every  existing  alternating  current  can  be  used,  is  fulfilled  only 
in  part,  for  each  furnace  operates  best  at  a  given  potential,  hence 
a  set  of  stationary  transformers  are  required  for  stepping  down 
voltages  as  high  as  22,000  directly  to,  say,  no  at  the  furnace. 
The  use  of  transformers  with  arc  furnaces  is  almost  universal. 

xTon  of  2,000  Ib.  avoirdupois. 


170      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Seldom  with  modern  installations  is  the  furnace  directly  con- 
nected with  its  own  generator,  although  this  was  much  in  vogue 
in  the  early  years  of  commercial  arc  furnaces.  The  frequency 
or  phase  with  this  furnace  is  immaterial,  and  does  not  affect 
its  operation.  That  the  roof  is  pierced  only  once  is  of  advantage, 
as  two  or  more  electrodes  coming  through  here  weaken  the 
arch,  even  if  it  is  dome-shaped.  The  electrodes  at  the  sides  in 
a  3-ton  furnace,  for  instance,  are  18  ins.  over  the  slag  line  when 
in  their  horizontal  position.  They  are  tilted  down  from  7  to 
17  degrees  for  the  operating  condition,  and  thus  allow  of  a  free 
view  of  the  hearth,  never  being  nearer  than  3  ins.  over  the 
bath  and  as  high  as  18  ins.  when  in  the  horizontal  position. 
They  can  also  be  tilted  upward,  about  7  degrees  being  enough, 
to  allow  of  a  larger  charge  in  the  beginning,  and  when  the  bath 
is  melted  this  additional  space  between  the  side  electrodes  and 
the  molten  metal  is  appreciated  by  those  rabbling  off  the  slag. 
This  tilting  of  the  side  electrodes  is  accomplished  by  turning  a 
small  hand-wheel. 

From  the  first,  all  Rennerfelt  furnaces  have  been  able  to 
avoid  sudden  power  fluctuations,  owing  to  the  fact  that  the  arc 
is  made  between  three  points  of  comparative  stability,  in  com- 
bination with  the  fact  that  the  arc  is  forced  down  upon  the 
bath  by  means  of  the  preponderating  power  of  the  current  in 
the  top  electrode.  Stassano  had  three  electrodes  with  three- 
phase  current,  but  his  power  fluctuations  were  most  violent,  as 
the  current  surged  continuously  from  one  electrode  to  another 
in  a  most  irregular  fashion,  due  no  doubt  to  the  absence  of 
any  of  the  electrodes  having  a  greater  electromagnetic  action 
in  one  direction  than  in  another,  i.e.,  the  Stassano  arc  is  in 
perpetual,  unstable  equilibrium  whereas  the  Rennerfelt  is  the 
exact  opposite  insofar,  and  yet  both  are  pure  radiating  arcs. 
When  melting  cold  material  no  great  power  fluctuations  occur, 
as  shown  by  the  curve  Fig.  65^.  Not  much  better  regulation 
could  be  obtained,  but  the  labor  of  one  man  could  be  saved 
by  using  automatic  regulators,  such  as  the  Thury  regulator. 

Easy  regulation  of  the  electric  power  is  obtained  with  this 
as  with  other  arc  furnaces. 


THE  RENNERFELT  FURNACE  171 

The  electrical  efficiency  of  this  furnace  is  about  the  same  as 
with  other  arc  furnaces  having  three  electrodes  above  the  bath. 
There  are  the  usual  electrode  losses,  about  7%,  as  already  dis- 
cussed for  this  furnace,  besides  the  transformer  losses,  3%. 

The  demand  that  the  furnace  be  of  the  tilting  variety  is 
easily  met  and  the  hearth,  being  circular,  with  one  or  two  doors, 
is  accessible  and  easily  surveyed. 

Even  though  the  carbon  vapor  with  its  reducing  action  may 
hinder  the  dephosphorization  with  its  necessary  oxidizing  con- 
dition, yet  repeated  practice  shows  there  is  no  difficulty  what- 
ever in  reducing  phosphorus  to  its  lowest  limits,  i.e.,  .002  and 
under,  with  as  low  a  power  consumption  as  any  other  arc  furnace, 
substantially  as  discussed  in  the  second  paragraph  of  the  book. 

Concerning  the  motion  of  the  charge,  there  is  only  that  due 
to  thermal  action,  the  same  as  in  an  open  hearth,  all  the  heat 
coming  from  above. 

The  application  of  the  furnace  has  a  wide  scope;  besides 
treating  steel,  gray  iron  scrap  and  melting  ferro-manganese, 
is  also  largely  used  in  the  various  copper-melting  and  nickel 
trades.  Cold  stock  is  as  easily  melted,  as  it  is  to  treat  hot 
metal.  Miscellaneous  steel  scrap  of  any  sized  pieces  which  can 
be  charged  through  a  door  457  X  508  mm.  (18  X  20  ins.)  is 
rapidly  melted  without  any  more  fluctuation  than  if  there  were 
only  the  smallest  pieces,  because  the  charge  is  not  in  the  electrical 
circuit  at  any  time.  The  Rennerfelt  has  so  far  only  been  built 
in  sizes  of  three  tons  or  so,  and  these  furnaces  are  operating 
well  both  here  and  abroad.  The  life  of  the  roof,  through 
which  only  one  of  the  three  electrodes  comes,  varies  much 
with  the  class  of  service,  the  experience  of  the  crew  and  the 
quality  of  the  refractories.  With  continuous  operation  and 
a  magnesite  roof  and  bottom,  melting  cold  charges,  as  much 
as  192  heats  from  one  roof  have  been  obtained.  With  acid 
refractories  throughout  and  intermittent  service,  i.e.,  twelve 
hours  or  so  daily,  346  heats  have  been  obtained  with  a  high- 
powered  furnace.  A  roof  lasts  many  weeks,  depending  upon 
the  conditions,  and  with  a  3-ton  furnace  with  silica  brick 
costing  $50  a  thousand  equals  $38  for  material.  The  cost  of 


172      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

all  refractories  with  an  acid  hearth  in  such  cases  is  about  70  to 
80  cents  per  ton  of  metal  poured.  Carborundum  (C  Si)  arch 
brick,  covered  by  a  layer  of  silica  arch,  and  sometimes  by  Kiesel- 
guhr  brick,  have  lasted  over  200  heats.  With  an  experienced 
crew  a  silica  roof  is  cheaper,  and  with  careless  operators  the 
carborundum  brick  roof. 

The  electrode  consumption,  when  using  Acheson  graphite, 
varies  considerably  with  conditions.  The  amount  of  air  leaking 
into  the  furnace  at  the  side  electrode  cooling  boxes  wears  them 
away  perhaps  more  than  any  other  thing,  hence  these  apertures 
are  kept  tight  by  means  of  asbestos  washers.  The  electrodes 
should  not  be  too  large,  as  the  wear  also  depends  upon  the 
surface  exposed.  High-powered  furnaces  making  quicker  heats 
consequently  use  less  electrodes,  other  things  being  equal;  2.5 
to  3.5  kg.  (5.5  to  7.7  Ibs.)  per  ton  of  cold  metal  charged  is  com- 
mon with  the  best  practice.  This  does  not  include  breakages, 
which  can  be  avoided  by  taking  proper  precautions. 

Slags  can  readily  be  changed  and  necessitate  80  to  90  Kw.hr. 
per  ton  for  each  additional  slag  with  ordinary  basic  steels. 
With  tool  steels  more  power  is  usually  consumed. 

The  thermal  efficiency  does  not  depend  so  much  on  the 
furnace  size  as  formerly,  mainly  on  account  of  the  power  now 
placed  on  these  furnaces.  For  instance, 

The  i  ton  has  300  to  400  Kw. 

"       2      "        "      S00    "    600      " 

"    3    "     "    600  "  900    " 

Larger  furnaces  are  contemplated,  using  more  than  one  set  of 
electrodes.  The  efficiency  is  greatly  increased  if  the  operation 
is  continuous,  twenty-four  hours  daily  for  the  week,  instead  of 
shutting  down  each  night,  even  though  for  only  a  few  hours. 
If  a  furnace  is  shut  down  overnight,  the  first  heat  usually  takes 
200  and  the  second  100  Kw.hr.  more  per  ton  than  the  third  or 
fourth  heats,  which  are  usually  normal.  This  can  be  consider- 
ably cut  down  by  heating  the  furnace  with  an  oil  or  gas  burner 
during  the  idle  period.  The  maximum  efficiency  can  be  regarded 
as  approaching  75%  when  operating  under  a  combination  of 
most  favorable  conditions. 


THE  RENNERFELT  FURNACE  173 

The  installation  costs  of  Rennerfelt  furnaces  vary  considerably. 
A  3 -ton  furnace  complete  in  every  respect,  ready  to  operate, 
complete  with  900  KVA.  in  transformers,  including  a  heavily 
discounted  royalty,  is  $37,250.  A  i-ton  under  similar  con- 
ditions costs  $18,800.  These  furnaces  are  also  sold  without 
transformers  and  also  under  royalty  conditions,  both  reducing  the 
initial  investment. 

All  Rennerfelts  operate  from  polyphase  current  and  from 
various  frequencies  •  from  25  to  60.  Hand  regulation  of  the 
electrodes  is  usually  sufficient  and  automatic  electrode  regulation 
would  be  an  additional  cost  of  about  $1,500  per  furnace.  The 
costs  are  exclusive  of  foundations,  installation  costs,  transformer 
room,  etc. 

The  advantages  which  Rennerfelt  himself  gives  over  other 
arc  furnaces  may  here  be  cited : 

1.  The  heat  is  generated  with  an  arc  with  the  absence  of 
exceedingly  hard  strains  on  the  power  supply. 

2.  On  account  of  the  steady  power  and  because  of  the  large 
flame  widely   diffused   and  violently    directed   downwards    as 
shown  on  Fig.  69,  the  heat  is  communicated  to  the  charge  quicker 
than'  with  arcs  of  the  thin  pencilled  type,  made  between  the 
tips  of  the  electrode  and  the  bath;  besides  this  the  arc  distance 
above  the  bath  is  variable, .  the  flame  size  and  power  remaining 
the  same  or  not  as  desired,  thus  increasing  or  decreasing  the 
mushrooming  effect  of  the  flame  on  the  bath  or  material  being 
melted  or  treated. 

3.  The  furnace  operates  with  polyphase  current,  and  yet  is 
only  pierced  once  through  the  roof  by  an  electrode;  thus  the 
roof  is  stronger  than  if  two  or  more  electrodes  made  holes  through 
the  roof  necessary. 

4.  The  heat  gradient  in  an  electric  arc  is  greater  if  it  takes 
place  in  the  widely  spread  out  zone  rather  than  in  a  narrow 
space,  and  the  radiating  arc  is  a  more  rapid  way  of  transmitting 
heat  than  with  the  shorter  flame  arc. 

5.  There  is  no  water  cooling  below  the  bath,  which  conse- 
quently avoids  danger  from  explosion  from  this  source. 

6.  The  arc  being  "free  burning,"  i.e.,  sustained  between  the 


174   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


r«Mll  -«.-*Ci  J 


I--*-  ''-UL 

'    trw* 


i  ~ 


THE  RENNERFELT  FURNACE  175 

tips  of  three  electrodes,  the  electric  flame  can  be  kept  in  the 
furnace  when  there  is  no  metal  on  the  hearth. 

These  claims  should  be  compared  with  the  advantages  put 
forth  by  Heroult  and  Girod,  as  mentioned  in  their  respective 
chapters. 

The  first  Rennerfelt  was  built  like  a  barrel  lying  on  its 
curved  surface  and  the  side  electrodes  coming  through  the  flat 
ends.  The  models  soon  following  kept  the  barrel  shape  but 
had  a  door  at  one  flat  end,  lying  on  the  curved  surface  as  before, 
but  the  side  electrodes  piercing  the  curved  surface  of  the  cylinder. 
Next  came  the  square  shell  and  the  rectangular  brick  work, 
then  the  rounded  brick  work  in  the  square  shell,  and  lastly 
the  inevitable  model  approximating  more  nearly  a  sphere  than 
all  other  models,  viz.:  the  cylindrical  shape  like  an  upright 
barrel,  with  or  without  a  truncated  bottom,  and  always  now 
with  a  dome-shaped  roof,  the  side-tilting  electrodes  piercing  the 
curved  sides.  Fig.  65  e  shows  this  latest  model  with  the  side 
electrodes  shown  at  the  maximum  tilting  angle  downwards. 
They  can  be  tilted  upwards  also  and  consequently  pass  through 
the  horizontal  position,  which  is  now  no  longer  their  only 
position. 

The  use  to  which  the  Rennerfelt  has  been  put  is  shown  in 
the  table  of  statistics.  Licenses  may  be  obtained  in  Sweden 
from  the  Aktiebolaget  Elektriska  Ugnar,  Stockholm,  for  prac- 
tically all  of  Europe,  and  in  the  United  States  by  American 
Transmarine  Co.,  Inc.,  New  York.1 

1  See  A.  E.  S.  XXIX— 1916— "  The  Rennerfelt  Electric  Arc  Furnace,"  by 
C.  H.  Vom  Baur. 


CHAPTER  XI 
THE  INDUCTION  FURNACE  IN  GENERAL 

IT  was  demonstrated  in  Chapter  IV  that  an  insulated  wire 
of  a  coil  carrying  current  generates  lines  of  force,  and  that  these 
lines  or  fields  of  force,  are  continually  alternating,  when  alternat- 
ing current  flows  in  the  coil.  These  alternating  lines  of  force 
constitute  the  well-known  underlying  principle  for  all  induction 
phenomena.  It  is  therefore  evident  that  in  an  electrical  con- 
ductor which  lies  in  the  field  of  another  conductor,  a  current  will 
be  induced,  which  will  be  proportional  to  the  number  of  lines  of 
force  cut  in  unit  time. 

This  fact  immediately  gives  us  the  information,  by  the  aid  of 
which  we  are  enabled  to  obtain  any  current  strength  by  induction. 
We  merely  have  to  oversee  that  the  conductor  in  which  we  desire 
to  induce  the  current  shall  be  cut  with  as  many  lines  of  force  in 
unit  time,  as  will  give  the  wished-for  current  conditions. 

In  order  to  achieve   this  we  encounter  these  various  possi- 
bilities: 

Imagine  a  certain  number  of  lines  of  force,  raised  to  twice 
their  strength.  Then  we  should  find  that  a  turn  of  wire,  lying 
in  this  magnetic  field,  would  have  twice  the  electro-motive  force 
generated  in  it  as  in  a  field  of  only  the  original  strength.  When 
the  magnetic  lines  are  doubled,  then,  the  conductor  is  cut  with 
twice  the  number  of  lines  of  force  in  the  same  time. 

The  same  effect  is  accomplished,  however,  when  the  field  is 
kept  at  its  original  strength,  if  two  turns  are  used  instead  of  one, 
where  they  are  both  cut  by  the  same  number  of  lines  of  force. 
What  we  have  then  in  this  case  is  an  increasing  number  of  turns, 
and  with  it  a  raise  in  the  voltage  in  the  induced  coil;  because 
for  the  moment  we  may  think  of  these  two  turns  as  being  sepa- 
rated in  such  a  way,  so  as  to  give  us  two  separate  turns,  each 

176 


THE  INDUCTION  FURNACE   IN  GENERAL  177 

having  the  same  voltage  that  one  turn  has  now.  Finally  the 
potential  in  the  induced  circuit  may  be  increased,  by  raising  the 
velocity  of  the  current  alternations,  and  this  leads  us  to  a  change 
in  the  frequency.  And  as  the  induced  voltage  is  proportional 
to  the  velocity  of  the  alternating  lines  of  force,  it  is  evident  that, 
a  current  of  50  cycles  will  give  twice  the  induced  voltage  a 
current  of  25  cycles  will  give,  other  things  being  equal. 

If  we  now  combine  the  three  methods  into  a  formula,  which 
influence  the  conditions  in  an  induced  circuit,  we  obtain  — 

e=CXvXsXN 
where  e  denotes  the  voltage 

v  denotes  the  frequency 

s  denotes  the  number  of  turns 

N  denotes  the  number  of  lines  of  force 
and  C  is  a  constant. 

We  have  so  far  assumed  that  our  lines  of  force,  generated 
by  the  aid  of  a  wire  coil,  sought  their  paths  through  the  air. 
This  arrangement  is,  however,  very  disadvantageous  because 
the  air  is  a  very  poor  magnetic  conductor  (being  only  1/180  as 
good  as  iron).  The  lines  of  force  in  this  way  seek  the  shortest 
path,  resulting  in  the  consequences  (for  instance,  with  a  coil  of 
a  great  number  of  turns)  that  only  a  part  of  the  turns  are  cut 
by  the  total  number  of  lines  of  force,  whereas  for  the  remaining 
turns  only  a  part  of  the  total  lines  are  taken  into  consideration 
at  all.  In  order  to  keep  the  lines  of  force  from  spreading,  or 
straying,  as  it  is  called,  we  provide  a  good  magnetic  conductor 
for  them,  which  forces  them  to  take  advantageous  and  prede- 
termined paths,  due  to  the  high  magnetic  conductivity,  which 
in  turn  gives  a  good  inductive  action.  These  things  give  us 
the  so-called  transformer. 

Fig.  66  shows  the  principal  arrangement  of  a  transformer 
as  it  is  commonly  used,  as  well  as  for  induction  furnaces.  In  the 
figure,  A'i  and  K2  denote  the  transformer  cores,  and  J\  and  J* 
the  yokes.  The  wire  coils  are  wound  on  these  cores.  The  coil 
receiving  the  current  from  an  outside  source  is  called  the  primary, 
and  the  coil  delivering  the  useful  current  is  called  the  secondary 


178  ELECTRIC  FURNACES  IN  THE  IR'ON  AND  STEEL  INDUSTRY 

winding.     Both  coils  are  separated  from  each  other  by  suitable 
insulation. 

If  these  yokes  and  cores  were  made  from  solid  pieces  of  iron, 
then  it  would  not  be  possible  to  avoid  the  considerate  losses  due 
to  eddy  currents,  as  set  forth  in  Chapter  IV.  Therefore,  in 
order  to  bring  these  losses  down  to  the  smallest  percentage,  the 
iron  cores  and  yokes  are  built  up  of  many  thin  sheets  of  iron  of 


FIG.  66. 


FIG.  67. 


.3  to  .5  mm.  (.012  to  .02  inches)  thick.  These  sheets  are  insulated 
from  each  other  by  pasting  sheets  of  paper  on  one  side,  about 
i/ 10  as  thick  as  the  sheet  iron,  and  the  whole  then  held  together 
by  means  of  screws.  Large  core  cross-sections  are  divided  into 
separate  divisions,  which  are  kept  apart  by  so-called  ventilating 
ducts,  by  means  of  which  the  already  low  hysteresis  and  eddy 
current  losses  and  their  consequent  heat  generation  are  nullified. 
Fig.  67  shows  one  of  these  core  cross-sections. 

If  the  primary  coil  of  a  transformer  is  energized  with  an 
alternating  current,  which  must  necessarily  produce  an  induced 
current  in  the  closed  secondary  circuit,  then  the  iron  core  will  be 
permeated  with  magnetic  lines  of  force,  which  is  common  to  both 
coils.  As  the  primary  and  secondary  coils,  besides  this,  must 
have  the  same  frequency,  we  obtain  the  equations  for  the  volt- 
ages in  both  coils,  as  follows: 


=  C  X  v  X  N  X 


and 


THE   INDUCTION   FURNACE   IN   GENERAL  179 

from  which  it  follows  that;  — 


In  this  ratio  we  call  the  factor  —  the  ratio  of  transformation. 

si 

The  equation  signifies  that:  — 

The  voltage  is  proportional  to  the  number  of  turns. 

By  applying  a  different  number  of  turns  in  a  transformer, 
we  obtain  a  means  whereby  any  existing  voltage  may  be  changed 
into  any  other  voltage,  and  one  thus  suitable  for  the  operation  of 
electric  induction  furnaces. 

In  this  way  transformers  are  nearly  always  used  in  alternating 
current  installations.  For  this  method  makes  it  possible  to 
transmit  power  over  great  distances  at  high  voltages  and  at 
small  currents,  thus  using  only  smaller  and  cheaper  conductor 
cross-sections,  from  the  central  station  to  the  point  of  power 
consumption.  At  that  place  then  a  transformer  is  erected,  by 
the  aid  of  which,  the  high  primary  voltage  is  changed  to  any 
desired  secondary  voltage,  which  may  be  most  advantageous 
for  the  particular  apparatus. 

We  have  already  observed  that  transformers  are  used  in  this 
way  for  arc  furnace  installations.  Alternating  current  provides 
such  a  convenient  way  of  transforming  energy  in  stationary 
transformers,  and  this  together  with  its  lack  of  chemical  influence 
constitute  the  two  factors  responsible  for  the  reason  that  all  arc 
furnaces  are  operated  with  alternating  current  to-day. 

With  the  present  technical  perfection  of  the  transformer 
this  last  may  be  regarded  as  a  sort  of  interposed  apparatus, 
which  produces  at  a  different  voltage,  almost  the  same  amount 
of  energy  which  it  receives.  That  is  to  say,  the  losses  in  a  trans- 
former are  extraordinarily  small.  With  transformers  of  more 
than  50  kw  the  losses  are  from  2  to  a  maximum  of  3%.  Even 
though  the  efficiencies  of  transformers  for  electric  furnaces  will 
fall  slightly  on  account  of  the  necessary  overload  capacity,  yet 
we  may  consider,  for  the  sake  of  simplicity,  that  the  total  primary 
power  is  given  up  in  the  secondary  circuit. 


180   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Then  the  primary  power  pi  =  e\  ii, 

and  the  secondary  power  pi  =  e2  iv, 

where  pi  =  p*  and  consequently  e\  i\  =  eziz- 

From  this  it  follows  that 

4  _  *  _  ±  that  is:_ 

12  Ci  Si 

The  current  is  inversely  proportional  to  the  voltage  and  inversely 
proportional  to  the  number  of  turns. 

The  foregoing  conclusion  is  of  the  greatest  importance  for  it 
solves  the  building  problems  of  induction  furnaces.  Induction 

furnaces  in  reality  are 
nothing  more  nor  less  than 
properly  designed  special 
transformers.  Hence  every 
induction  furnace  has  its 
iron  core  and  yoke,  to 
carry  the  lines  of  force, 
and  a  primary  winding, 
wound  over  one  part  or 
another  of  the  iron  core. 
FIG.  68.  FIG.  69.  On  the  other  hand,  the 

secondary  winding  is  com- 
posed either  entirely  or  for  the  most  part  of  the  bath  itself. 

This  point  of  view  enables  us  to  group  electric  induction 
furnaces — on  the  one  hand  into  those  furnaces  where  the 
secondary  winding  is  composed  entirely  of  the  bath,  and  on  the 
other  hand  into  those  where,  besides  the  bath  being  the  secondary 
winding,  there  is  still  another  winding,  made  of  copper  to  aid 
the  heating.  We  denote  the  former  as  simple  induction  furnaces 
and  the  latter  as  combination  furnaces. 

If  we  take  up  the  first  group  of  simple  induction  furnaces, 
we  see  that  the  different  methods  of  construction  can  be  dis- 
tinguished merely  by  the  way  the  primary  coil  is  placed,  relative 
to  the  bath.  The  Figs.  68  to  72  show  a  number  of  the  most 
prevalent  suggestions.  In  the  figures  the  steel  bath  is 
denoted  by  the  solid  black,  (the  layer  of  slag  is  not  shown,) 


THE   INDUCTION  FURNACE  IN  GENERAL  ]8l 

the  refractories  by  inclined  hatching  and  the  primary  winding 
by  cross  hatching.  Figs.  68  and.  69  show  the  primary  winding 
in  the  form  of  large  radial  disks,  which  are  under  or  over  the  bath, 
or  as  Fig.  68  shows  it  to  be  both  under  and  over  the  metal.  On 
the  other  hand,  Figs.  70  and  72  shows  the  primary  winding  in  the 
form  of  a  long  cylinder,  which  is  placed  inside  or  outside  of  the 
ring-shaped  hearth.  With  this  arrangement  we  speak  of  a 
transformer  with  cylinder  or  tube  winding  and  those  of  Figs.  68 
and  69  as  having  a  disk  winding. 

In  all  cases  the  principle  of  transforming  the  energy  is  the 
same,  and  in  all  cases  we  shall  find  the  ring  form  hearth,  in  whose 
contents  the  heating  currents  are  produced  by  means  of  induction, 
quite  independent  of  the  place  in  the  magnetic  circuit,  occupied 
by  the  primary  winding.  It  is  evident  that  any  of  these  winding 
schemes  can  be  combined  with  every  other  method,  and  we  may 
therefore  state  that  there  is  no  combination  of  windings  and 
no  placing  of  it  at  some  part  of  the  transformer,  that  has  not 
already  been  patented  as  being  particularly  good. 

It  has  been  shown  that  we  are  enabled  to  obtain  any  desired 
current  strength  in  the  secondary  circuit,  by  properly  winding 
the  primary.  The  first  one  to  recognize  these  conditions  and 
use  them  in  the  design  of  an  electric  furnace  was  de  Ferranti1, 

1  In  this  connection  proper  credit  must  also  be  given  to  Colby.  Many 
years  after  the  invention  was  made,  the  Franklin  Institute  investigated  the 
early  patent  applications  of  both  Ferranti  and  Colby  and  reported,  in  1911, 
in  part,  in  speaking  of  the  patents,  as  follows: 

See  British  patent  to  Ferranti,  No.  700,  Dec.  16,  1887,  filed  January  15, 
1887. 

U.  S.  Patent  to  Colby,  No.  428,378,  May  20,  1890,  filed  April  14,  1887. 

U.  S.  Patent  to  Colby,  No.  428,379,  May  20,  1890,  filed  Sept.  19,  1887.  .  .  . 

Between  the  years  1890  and  1900  no  notable  application  of  the  process 
appears  to  have  been  made.  .  .  . 

Colby's  furnace  is  most  broadly  described  in  his  U.  S.  Patent  428,379. 

It  appears  evident  that  the  applicant  was  one  of  the  first  to  devise  the 
elemental  features  of  the  induction  furnace.  .  .  . 

It  is  generally  conceded  that  the  basic  use  of  the  transformer  principle  to 
electric  furnaces  was  independently  applied  by  both  Ferranti  and  Colby,  the 
dates  of  their  patent  applications  being  but  a  few  months  apart.  The  tubular 
water-cooled  conductors,  the  means  of  supporting  them  and  the  connecting 
devices  constitute  essentially  the  features  of  novelty  in  the  most  recent  patent 


182   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

who  patented  his  apparatus,  as  shown  schematically  by  Fig. 
68,  in  1887.  Even  though  his  design  was  never  put  to  practical 
use,  we  see  how  completely  de  Ferranti  and  Colby  had  at  that 
time  mastered  the  problem  of  heating  by  induction  currents. 

If  we  use  the  furnace  form  as  shown  in  Fig.  68,  in  order  to 
obtain  a  clear  view  of  induction  heating,  we  observe  that  the 
middle  core  of  the  transformer  carries  the  primary  winding  and 
that  the  furnace  hearth  is  arranged  concentric  with  this.  There 

of  Colby.  .  .  .  The  forms  of  induction  furnace  depicted  in  the  early 
Colby  patents  closely  resemble  those  adopted  in  present-day  apparatus  and 
although  but  a  joint  pioneer  in  this  field,  his  original  designs  are  distinctive 
in  anticipating  the  subsequent  state  of  the  art. 

In  consideration  of  its  originality  and  wide  and  successful  commercial  use, 
the  Institute  recommends  to  the  Philadelphia  Board  of  City  Trusts  the  award 
of  the  John  Scott  Legacy  Premium  and  Medal  *  to  Edward  Allen  Colby  of 
Newark,  N.  J.,  for  his  Induction  Electric  Furnace. 

Adopted  at  the  Stated  Meeting  of  May  3,  1911. 

(Signed)  WALTER  CLARK,  President, 
R.  R.  OWENS,  Secretary. 

GEO.  A.  HOADLEY,  Chairman  of  the  Committee  on  Science  and  the  Arts. 

*  Medal  shown  herewith: 


FIG.  690. — Facsimile  of  medal  awarded  to  Colby  for  his  induction 
furnace  by  the  Franklin  Institute. 


THE  INDUCTION  FURNACE  IN  GENERAL  183 

is  no  secondary  winding  of  copper  such  as  we  usually  find  with 
ordinary  transformers.  Should  the  ring-shaped  hearth  be  filled 
with  molten  iron,  as  shown  in  the  figure,  we  may  regard  this  ring 
of  iron  as  the  secondary  winding,  which  is  composed  of  only  one 
single  turn.  Induced  currents  will,  therefore,  appear  in  this 
iron  ring,  the  same  as  they  would  in  every  other  electrical  con- 
ductor which  lies  in  an  alternating  current  magnetic  field. 

As  the  iron  ring  comprises  in  itself  one  short-circuited  turn — 
or  a  short-circuit — consequently  all  of  the  energy  of  the  secondary 
circuit  is  transformed  into  heat,  as  the  secondary  current  has 
to  overcome  the  resistance  of  the  iron  bath.  The  heat  quantity 
generated  is  proportional  to  r  r,  that  is,  it  is  proportional  to  the 
product  of  the  square  of  the  current  and  the  resistance.  As  the 
resistance  of  the  iron  bath  may  be  regarded  as  being  practically 
constant  for  a  given  charge,  it  is  evident  that  any  desired  tem- 
perature may  be  obtained1  by  raising  the  current  and,  of  course, 
first  of  all,  by  a  proper  choice  of  the  primary  turns;  for  the 
secondary  turns  with  these  furnaces  are  always  equal  to  unity. 

Suppose  we  had  an  induction  furnace,  possessing  100  turns 
in  its  primary  winding,  and  at  a  definite  voltage  of,  say  1000,  it 
took  100  amperes,  we  would  obtain  a  secondary  current  value  of 

Si  100 

£2  =  i\  X  —  =  100. =  loooo  amperes. 

On  the  other  hand,  if  we  had  a  furnace  wound  with  120 
primary  turns,  and  taking  the  same  100  amperes  as  before,  but 
at  a  correspondingly  changed  voltage,  we  would  obtain  a  current 
of, 

Si  120 

*2  =  ti  X  —  =  ioo. =  12000  amperes,  in  the  bath. 

$2  I 

These  examples  show  how  the  number  of  turns  influences 
the  secondary  current,  and  consequently  the  attainable  tem- 
perature of  the  bath.  It  is,  therefore,  the  part  of  the  furnace 
designer  to  so  choose  his  proportions,  that  he  may  in  any  case 
reach  the  desired  temperatures,  for  his  particular  case. 

1  See  Am.  Electro-Chemical  Society,  Sept.,  1912,  paper  by  C.  H.  Vom  Baur 
on  "Electric  Induction  Furnaces  for  Steel,"  giving  an  instance  where  the 
temperature  of  steel  in  an  induction  furnace  reached  2550°  to  2600°  C. 


184  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

During  the  operation  it  is,  of  course,  precluded  that  any 
primary  turns  of  the  furnace  transformer  be  changed.  Still, 
during  the  time  of  operation,  temperature  changes  are  desired, 
which  in  turn  calls  forth  changes  in  the  energy  absorption  of 
the  furnace.  But  even  these  changes  are  easily  made.  We  have 
only  to  realize  that  the  load  on  the  furnace  transformer  is  brought 
about  solely  by  the  particular  resistance  of  the  iron  bath,  which 
we  may  consider  as  a  constant  factor  for  a  definite  charge.  It 

is  now  apparent  that  we  have  in  Ohm's  Law  i  =  —  ,  a  simple 

remedy  for  changing  the  energy,  and  thereby  the  current,  by 
simply  altering  the  voltage  for  the  primary  winding. 

Necessarily  the  secondary  voltage  and  its  current  are  instantly 

sz 
changed  as  e2  =  e\  — . 

If  we  now  review  the  above,  regarding  induction  furnaces,  we 
find:— 

1.  The  charge  in  induction  furnaces  is  heated,  solely  and 
alone  by  reason  of 'the  current  overcoming  the  opposed  resistance, 
and  to   any  practically  desired   temperature.     The   induction 
furnace  is  therefore  only  a  particularly  favorable  type  of  resis- 
tance furnace,  which  allows  a  complete  and  even  heating  of  the 
metal,  without  producing  any  overheating  at  any  point. 

2.  By  changing  the  primary  voltage  at  any  time  during  the 
operation  of  the  furnace,  the  temperature  of  the  charge  may 
be  raised  or  lowered  at  will,  either  quickly  or  slowly.     At  the 
same  time  the  heat  in  the  entire  furnace  contents  is  altogether 
uniformly  raised  or  lowered. 

If  all  induction  furnaces  possess  these  qualities,  what  differ- 
ences are  there  then  between  the  different  arrangement  of  the 
windings  as  far  as  the  molten  metal  is  concerned?  (See  Figs.  68 
to  72.) 

It  is  well  to  state  that  the  differences  between  Figs.  71  and 
72  are  purely  constructive,  as  the  double  magnetic  path  halves 
the  cross-section  of  Fig.  72,  opposite  the  simple  path  with  the 
whole  cross-section  of  Fig.  71,  yet  does  not  in  any  way  produce 
any  new  electrical  effects.  Therefore,  these  two  types  of  Kjellin 


THE   INDUCTION  FURNACE   IN   GENERAL 


185 


furnaces  only  differ  in  their  outward  appearance,  without  either 
one  or  the  other  of  the  iron  cores  giving  any  advantages  worth 
mentioning. 

Substantial  differences  may,  therefore,  only  be  found  in  the 
arrangement  of  the  coils,  and  these  follow  different  directions. 
It  is  evident  that  the  suggestion  of  Colby,  made  in  1887,  (the 


FIG.  70. 


FIG.  71. 


FIG.  72. 


first  to  surround  the  hearth  with  the  winding,)  necessitates  more 
copper  conductors  than  the  second  suggestion  of  Kjellin,  of  1900, 
where  the  primary  winding  is  inside  of  the  ring-shaped  hearth. 
The  whole  arrangement  of  the  Kjellin  furnace,  by  reversing  this 
idea,  is  simpler  than  the  Colby  furnace,  not  only  on  paper,  but 
also  in  reality.  The  Colby  furnace,  as  well  as  the  de  Ferranti 
furnace,  are  today  only  of  historical  importance,  except  for  their 
later  existing  patents.  This  leaves  only  the  accomplishments 
of  Kjellin  and  Frick  for  discussion. 

If  we  put  aside  for  the  moment  the  fact  that  the  Frick  furnace 
does  not  permit  such  a  general  view  of  the  hearth,  or  allow  the 
accessibility  thereto,  on  account  of  the  overhanging  disk  winding, 
as  we  have  with  the  Kjellin  furnace  with  its  coil  removed  from 
the  operating  conditions,  we  find  that  the  chief  distinction  be- 
tween these  furnaces  lies  in  the  different  circulation  of  the  bath, 
caused  by  the  changed  position  of  the  coil.  We  saw  in  Chapter 
III  that  the  motor  effect  of  an  electric  current  appears,  when  two 
conductors  with  their  magnetic  fields  mutually  affect  each  other. 
The  different  position  of  the  winding  cannot,  therefore,  be  with- 
out its  influence  on  the  inclination  of  the  bath  surface.  As  will 


186  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

be  shown  in  the  following  chapter,  the  Kjellin  furnace  produces 
the  effect  of  pressing  the  molten  metal  toward  the  outside,  so 
that  it  stands  higher  on  the  outside  wall  than  on  the  inside.  In 
the  Frick  furnace,  for  the  same  reason,  we  find  a  stronger  mag- 
netic pressure  on  the  current  carrying  molten  metal,  where  the 
bath  and  the  coil  are  nearest  to  each  other,  and  this  causes  the 
metal  surface  to  be  more  depressed  at  this  point  than  the  re- 
maining part  of  the  hearth.  The  Frick  furnace,  therefore,  also 
has  an  inclination  to  its  bath  surface,  so  that  this  stands  higher 
at  the  outside  than  at  the  inside.  While  this  slope  in  the  bath 
is  only  4°  34'  to  5°  5'  with  an  8-ton  Frick  furnace,  according  to 
the  published  report  of  von  Neumann  of  the  firm  of  Freidrich 
Krupp  (see  Stahl  und  Eisen,  1910,  p. '1071),  we  see  that 
with  a  Kjellin  furnace  of  the  same  size,  that  it  is  24°.  These 
differences  naturally  cause  considerable  deviation  in  the  circula- 
tion phenomenon  of  the  bath,  so  that  these  are  greater  in  the 
Kjellin  furnace  and  to  its  detriment,  than  they  are  in  the  Frick 
furnace. 

Even  though  there  are  certain  differences  between  the  Frick 
and  the  Kjellin  furnaces,  owing  to  the  different  position  of  the 
windings,  still  in  the  essentials  of  their  operation  they  are  en- 
tirely alike.  As  the  Kjellin  furnace  opposite  the  Frick  furnace 
has  found  a  much  more  extended  use,  it  will  suffice  if  we  describe 
the  Kjellin  furnace  in  the  next  chapter  as  a  representative  one. 
In  this  the  secondary  coil  is  composed  solely  and  alone  by  the 
hearth  metal  itself.  The  honor  is  due  Kjellin  for  producing  the 
first  practically  useful  induction  furnace. 

In  addition  to  the  group  of  induction  furnaces  just  men- 
tioned, in  which  the  secondary  coil  of  the  furnace  transformer 
is  composed  entirely  by  the  bath,  there  is  yet  a  second  group 
of  induction  furnaces,  which  has  another  common  copper 
winding,  besides  the  short  circuited  secondary  turn  which  is  the 
bath. 

This  second  group  of  induction  furnaces  owes  its  existence 
primarily  to  the  fact  that  the  furnaces  of  the  first  group  have  a 
comparatively  poor  power  factor.  The  cause  of  this  being  that 
the  distance  between  the  primary  and  secondary  windings  is  so 


THE  INDUCTION  FURNACE  IN  GENERAL  187 

great,  that  a  large  number  of  the  lines  of  force  take  their  path 
through  the  air,  without  being  able  to  affect  the  secondary  volt- 
age. We  designate  these  lines  of  force  as,  stray  lines  or  leakage 
lines,  and  the  phenomena  itself  is  called  magnetic  leakage,  and 
it  is  this  which  operates  heavily  against  the  power  factor. 

The  greater  the  distance  between  the  primary  and  secondary 
winding,  the  larger  the  magnetic  leakage  will  be,  and  the  lower 
the  power  factor.  The  leakage  may  be  lessened  by  placing 
conductors  in  the  path  of  these  leakage  lines,  in  which  secondary 
currents  are  generated  by  induction.  As  these  currents,  which 
are  generated  by  induced  currents,  always  have  the  opposite 
direction  of  the  primary  or  incoming  current,  (as  was  shown  in 
discussing  the  self-induction  phenomenon  on  page  44,)  they 
will  in  turn  send  out  stray  lines  of  force  in  the  opposite  direction 
into  the  original  stray  field,  and  in  this  stray  field  the  conductors 
lie.  We  may  look  upon  this  effect  as  one  where  the  stray  lines 
are  pushed  back,  and  in  this  way  the  power  factor  is  raised  by 
the  coils,  which  lie  in  the  space  between  the  primary  winding 
and  the  bath. 

Patents  show  a  large  number  of  suggestions,  in  which  second- 
ary copper  windings  are  to  be  employed,  in  order  to  gain  the 
above  result.  But  the  fact  must  not  be  overlooked  that  on 
the  one  hand  a  poor  power  factor  increases  the  initial  cost  but 
does  not  increase  the  energy  losses,  and  on  the  other  hand  the 
current  generation  in  the  secondary  winding  (to  decrease  the 
magnetic  leakage)  can  only  be  accomplished  with  energy  so  it 
is  immediately  evident  that  danger  lurks  nigh,  in  curing  a  small 
evil  with  a  larger  one.  This  error  is  shown  by  all  the  designs, 
whose  sole  object  it  is  to  lessen  the  stray  fields,  by  means  of  the 
secondary  copper  winding,  in  which  the  heat  which  is  generated 
in  these  coils  is  not  put  to  any  use;  on  the  contrary  this  results 
in  only  enlarging  the  cooling  appliances  for  the  windings,  in 
order  to  protect  them  from  too  high  a  temperature. 

The  idea  of  applying  the  above-mentioned  stray  field  reducing 
arrangements  to  induction  furnaces,  can  hardly  be  looked  upon 
as  induction  furnace  improvements,  (as  we  have  learned  to  know 
the  furnace  in  the  first  group,)  as  long  as  no  provision  is  made 


188   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

to  profitably  use  the  currents  generated  in  the  secondary  copper 
winding. 

This  last  requirement  is  fulfilled  by  the  Roechling-Roden- 
hauser  furnace,  and,  as  a  result,  these  furnaces  have  already  come 
into  quite  extensive  use,  whereas  all  other  suggestions  to  improve 
the  induction  furnace  power  factors  from  within  the  confines  of 
the  furnace  proper  are  today  only  on  paper. 

It  therefore  seems  sufficient  within  the  limits  of  this  book, 
besides  describing  the  Kjellin  furnace,  to  merely  narrate  the 
details  of  the  Roechling-Rodenhauser  furnace,  not  only  because 
these  two  are  the  only  induction  furnaces  having  found  ex- 
tensive use,  but  also  because  a  discussion  of  these  furnaces  will 
be  sufficient  to  give  the  reader  a  clear  idea  of  the  workings  of 
induction  furnaces.  At  the  same  time  it  will  also  enable  one  to 
adequately  judge  the  value  of  any  other  constructional  features. 

If  in  closing  we  again  mention  the  essential  thing  about  an 
induction  furnace,  we  find  that  the  characteristic  mark  of  them 
all  is  the  common  transformer. 

In  the  induction  furnace  we  find  the  application  of  the 
built-in  transformer  to  be  of  the  greatest  importance  to  the 
heating  method.  For  in  this  way  only  is  it  possible  to  generate 
the  strongest  currents  directly  in  the  iron  bath  without  con- 
duct or  losses,  so  that  the  molten  metal  itself  may  be  regarded 
as  the  source  of  heat. 

In  his  addresses  before  the  "Verein  deutscher  Eisenhiitten- 
leute,"  Borchers  says: 

"Here  in  the  induction  furnace  we  should  truly  possess  the 
most  perfect  of  electrical  heating.  Here  the  generation  of  heat 
goes  on  solely  and  alone  in  the  metal  to  be  melted,  and  in  the 
molten  bath:  the  heat  transference  from  other  heat  sources  to 
the  metal  is  not  first  required." 

Again  when  comparing  resistance  furnaces, — and  the  induc- 
tion furnace  may  be  regarded  as  a  resistance  furnace, — with  arc 
furnaces,  Borchers  says:  "With  both  furnaces  it  is  possible  to 
reach  a  temperature  of  3500°  C.  (6332°  F.).  There  will  always 
be  3500°  C.  at  the  arc  of  an  arc  furnace,  while  resistance  heating 
enables  any  temperature  up  to  this  point  to  be  reached." 


CHAPTER  XII 

THE   KJELLIN   FURNACE 

THE  first  induction  furnace  which  made  a  name  for  itself 
as  a  result  of  its  achievements  was  the  Kjellin  furnace.  It 
was  conceived  in  1899;  thus  the  first  trial  furnace  was  placed 
in  operation  on  March  18,  1900.  The  furnace  was  only  intended 
for  a  capacity  of  80  kg.  (176  Ibs.),  with  an  energy  consumption 
of  78  kw.  Steel  castings  could  be  made  with  this  furnace, 
only  with  the  extraordinarily  high  power  consumption  of  over 
7000  kw  hours  per  ton  of  steel.  With  the  second  furnace  of 
180  kg.  (about  400  Ibs.),  which  was  ready  for  operation  in 
November,  1900,  this  amount  was  reduced  to  one- third  of  the 
original  figure.  A  third  furnace  followed  having  a  capacity  of 
1350  (about  3000  Ibs.)  to  1800  kg.  (about  4000  Ibs.),  which  was 
installed  in  Gysinge  on  the  Dalelf  in  Sweden.  With  this  furnace 
they  succeeded  in  bringing  down  the  power  consumption  to 
about  800  kw.-hrs.  per  ton  when  making  steel  from  cold  scrap, 
and  thus,  the  Kjellin  furnace  proved  its  practical  and  economical 
adaptability. 

On  account  of  the  successful  operation  of  these  furnaces,  the 
Kjellin  patents  were  acquired  by  Siemens  &  Halske  A.-G.-  for 
the  principal  countries  of  Europe,  and  under  their  guidance 
these  furnaces  were  soon  used  to  a  considerable  extent. 

In  the  construction  of  the  Kjellin  furnace,  the  part  giving  it 
its  characteristic  appearance  is  the  transformer,  which  comes 
up  through  the  centre  of  the  ring-formed  hearth.  The  first 
successfully  useful  Kjellin  furnace  was  the  one  having  a  capacity 
of  1350  to.  1800  kg.  (about  3/4000  lb.).  This  furnace  is  shown 
in  its  later  design  in  Figs.  73  and  74.  The  original  is  of  the 
stationary  type.  The  transformer  consists  of  two  vertical  cores 
and  two  horizontal  yokes.  These  are  composed  of  thin  iron 


190   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

sheets,  paper  insulated,  of  the  usual  transformer  construction, 
so  that  the  magnetic  losses  are  as  low  as  possible.  Whereas  the 
yokes  and  the  unwound  core  of  the  transformer  have  a  rec- 


FIG.  73. 

tangular  cross-section,  the  core  carrying  the  primary  winding  is 
made  in  the  form  of  a  cross  (see  Figs.  67, 73  and  84).  This  arrange- 
ment permits,  on  the  one  hand,  a  saving  in  the  copper  winding, 

i 


FIG.  74. 


THE  KJELLIN  FURNACE  191 

as  the  core  is  of  circular  form  and  easily  wound,  on  the  other,  it 
provides  for  successful  cooling  of  the  transformer  iron  on  account 
of  its  larger  surface  and  thus  favorable  cooling  conditions  are 
provided.  For  this  Kjellin  with  his  first  1^2 -ton  furnace,  used 
four  one-inch  tubes  which  were  placed,  one  each  in  the  recesses 
made  by  the  section  of  cross  form.  These  tubes  carried  an  air 
circulation  of  40  mm.  (1.6  inches)  water  gauge  pressure  in  this 
winding  space,  which  was  thus  kept  at  permissible  temperature. 
This  air  cooling  was  also  taken  from  the  normal  transformer 
design  and  utilized  in  this  special  construction  of  furnace  trans- 
former. Besides  this,  in  order  to  shield  the  transformer,  and 
especially  the  coil  from  the  radiated  heat,  (from  the  furnace 
refractories,)  the  latter  is  surrounded  with  a  double  walled 
cylinder  of  brass  of  ij^  mm-  (-06  inches)  thickness.  Either 
cooling  water  or  air  is  passed  through  this  protective  cooling,  in 
order  to  keep  the  heat  from  the  winding  and  the  transformer. 
The  temperature  of  the  cooling  water  coming  from  the  pro- 
tective cylinder  was  measured  during  operation  and  showed  40 
to  50°  C.  Naturally  this  protective  cylinder  could  not  be  a  closed 
circuit,  or  if  so,  it  would  form  a  short  circuited  turn,  which  would 
become  heated  or  even  melted  under  the  influence  of  the  currents 
which  would  be  induced  in  it.  In  order  to  avoid  this  the  protect- 
ive shield  is  built  as  an  open  double  walled  ring,  while  in  the 
Kjellin  furnace  it  is  bridged  over  with  wood  insulation.  On 
the  outside  of  these  cylinders  we  find  the  furnace  refractories 
or  the  brick  work,  in  which  there  is  a  ring-shaped  space  concentric 
with  the  winding,  which  comprises  the  furnace  hearth.  The 
furnace  shell  is  of  sheet  iron  and  encloses  both  cores  of  the  trans- 
former. 

After  the  protective  brick  work  has  been  placed  in  tne 
furnace,  the  bottom  is  rammed  in.  Then  a  templet  having 
the  shape  of  the  hearth,  is  lowered  into  the  furnace,  so  that  the 
hearth  walls  of  suitable  material  may  be  tamped  in.  When 
this  work  is  finished  the  templet  is  raised  and  the  hearth  is 
practically  ready.  The  hearth  roof  consists  of  special  bricks, 
or  of  small  refractory  arches  held  in  iron  frames,  so  that  they 
may  be  easily  removed.  This  is  necessary  as  the  furnace  has 


192  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

no  doors,  and  the  hearth  and  the  progress  of  the  charge  can 
therefore  only  be  watched  by  lifting  off  one  or  more  covers. 
When  the  furnace  is  made  of  the  stationary  type,  it  must  neces- 
sarily have  the  stationary  type  spout. 

Subsequent  to  the  design  of  the  first  Kjellin  furnace  as  just 
described,  the  following  constructive  changes  were  made: 

In  order  to  allow  of  a  thorough  cooling  of  the  transformer,  it 
was  divided  into  a  number  of  smaller  divisions,  which  were 
separated  by  means  of  suitable  air  spaces.  This  was  only 
following  good  transformer  practise,  and  the  separate  sheets 
were,  of  course,  paper  insulated  as  usual.  The  air  cooling  was 
changed  so  that  there  was  a  more  uniform  cooling,  not  only  of 
the  transformer  iron,  but  also  of  the  coil. 

The  water  cooling  of  the  protective  cylinder  was  avoided 
and  air  cooling  substituted,  this  coming  from  the  same  ventilating 
fan  feeding  the  coils.  This  simplified  the  furnace  construction 
considerably,  and  gave  equally  safe  operating  conditions. 

The  furnace  was  made  of  the  tilting  variety  which  materially 
bettered  the  conditions  for  teeming.  It  may  be  of  interest  to 
mention  that  Kjellin  furnaces  have  been  constructed  as  though 
they  were  self-heating  pouring  ladles,  with  which,  for  instance, 
the  metal  could  be  taken  from  the  open  hearth  furnaces,  then 
refined  and  finally  poured  from  the  furnace  directly  into  the 
ingot  moulds. 

The  operation  of  the  furnaces  is  primarily  influenced  by  the 
fact  that  the  molten  metal  serves  as  the  secondary  winding. 
Therefore  as  long  as  the  metal  does  not  possess  a  conductivity 
giving  an  operating  voltage  having  a  sufficient  heating  current, 
the  heating  of  the  furnace  by  electrical  means  is  impossible. 
These  conditions  are  the  determining  factors  for  the  heating 
of  the  furnace.  As  the  hearth  is  of  the  ring  form,  it  is  not 
feasible  to  heat  the  furnace  with  coke.  Care  is  therefore  taken 
with  Kjellin  and  all  other  induction  furnaces  to  heat  them  up 
with  rings  of  material  later  to  be  melted.  For  making  steel, 
these  rings  may  be  cast,  welded,  or  even  screwed  together,  and 
laid  in  the  furnace.  As  soon  as  the  current  is  turned  on,  induced 
currents  arise  in  the  iron  rings,  as  they  become  short-circuited 


THE  KJELLIN  FURNACE  193 

secondary  windings.  The  iron  is  soon  brought  to  redness,  so 
that  the  heat  thus  produced  can  be  used  to  warm  up  the  furnace. 
As  soon  as  the  furnace  walls  are  red  hot,  the  furnace  is  charged 
with  fluid  metal,  and  the  heating  rings  are  subsequently  melted. 
When  this  is  accomplished,  the  furnace  soon  reaches  the  proper 
temperature  so  that  the  normal  furnace  operation  may  begin. 
If  the  furnace  is  operated  with  hot  charges,  as  is  often  the  case 
with  Kjellin  furnaces  operating  in  conjunction  with  open  hearth 
furnaces,  the  furnace  is  fully  emptied  after  each  charge  and 
then- charged  again  with  open  hearth  metal.  It  is  evident  that 
it  is  possible  to  fully  empty  the  furnace  after  each  charge.  Then 
when  the  fluid  metal  of  the  new  charge,  immediately  makes  a 
closed  ring  again,  the  heating  begins  simultaneously,  provided 
the  primary  circuit  is  closed. 

The  conditions  are  different  when  the  furnace  is  charged 
with  cold  material.  If,  under  these  conditions,  the  furnace  was 
completely  emptied,  and  a  ring  made  of  a  large  number  of 
pieces  of  cold  scrap,  its  resistance  would  be  so  great,  that  the 
proper  heating  currents  could  not  exist.  In  this  case,  it  would 
be  found  useless  to  try  to  obtain  a  melt.  It  might,  however, 
be  possible  to  raise  the  secondary  or  bath  voltage  sufficiently, 
so  that  arcs  would  appear  between  the  many  small  pieces  of 
scrap.  In  such  an  event  we  would  obtain  heating  methods 
similar  to  those  employed  when  melting  down  cold  scrap  in  the 
Girod  furnace.  The  raising  of  the  voltage  necessary  to  do  this, 
however,  leads  to  difficulties  in  the  transformer  design.  For 
this  reason,  therefore,  when  working  with  cold  stock,  a  sufficient 
portion  of  the  previous  charge  is  left  in  the  furnace  to  form  a 
closed  circuit.  If  the  furnace  is  now  further  charged  with  scrap, 
it  will  be  melted  down  by  the  heat  generated  in  the  metal  from 
the  previous  charge.  In  this  case  the  cross-section  of  the  bath 
grows,  and  a  greater  absorption  of  energy  takes  place,  thus 
hastening  the  melting.  A  very  quiet  melting  together  of  the 
charge  occurs  in  this  way,  without  any  sudden  power  fluctua- 
tions. As  there  is  always  a  molten  remainder  in  the  furnace 
when  using  the  method  of  cold  charging,  it  is  of  advantage  to 
keep  this  remainder  as  small  as  possible;  still  it  must  be  large 


194  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

enough  to  render  certain  the  closing  of  the  molten  secondary 
circuit.  The  smaller  the  section  of  the  lower  part  of  the  trough, 
the  easier  it  is  to  accomplish  this.  For  this  reason  it  is  well 
to  make  the  channel  V  -shaped. 

It  was  previously  mentioned  that  cold  charges  are  melted 
down  without  any  current  fluctuations  taking  place. 

We  now  come  to  the  electrical  conditions  existing  in  the  in- 
duction furnace.  If  we  look  a  little  closer  at  the  current  con- 
ditions of  the  Gysinge  furnace,  we  find  that  for  its  operation 
there  is  provided  a  300  HP  water-wheel  driving  a  direct  connected 
165  to  170  kw.  15  cycle,  single-phase  generator  of  3000  volts. 
When  the  furnace  content  is  1350  kg.  (about  3000  Ib.)  the 
power  factor  is  80%,  and  with  a  content  of  1800  kg.  (about 
4000  Ib.)  it  is  68%. 

Even  these  figures  show  the  dependence  of  the  power  factor 
on  the  size  of  the  charge  with  Kjellin  furnaces.  This  is  also 
substantiated  by  the  curve  in  Fig.  77,  which  was  made  from 
results  taken  from  a  Kjellin  furnace  having  a  maximum  capacity 
of  8>^  tons.  This  shows,  too,  how  (with  other  electrical  con- 
ditions remaining  the  same),  the  power  factor  becomes  lower 


^^^ 

. 

JJ.55 

0.7 

. 

FIG.  77. 

with  an  increased  charge.  We  can,  therefore,  establish  the 
fact  that: — "With  the  same  frequency  the  power  factor  falls  with 
an  increased  charge." 

In  searching  for  the  cause  of  this,  we  must  go  back  to  the 
causes  affecting  the  power  factor.  For  this  purpose  we  again 
reproduce  the  vector  diagram  originally  shown  as  Fig.  30  in 


THE  KJELLIN  FURNACE 


195 


Chapter  IV.  We  see  that  the  size  of  the  angle  <£  depends  on  the 
resistance  of  the  bath  r  and  again  upon  the  factors  m  and  L,  In 
our  examples,  in  both  of  which  the  periodicity  remains  the  same, 
the  factor  m,  depending  upon  the  latter,  also  remains  unchanged. 
Therefore,  only  r  and  L  remain 
as  means  for  reducing  the  power  , 
factor. 

It  is  evident  from  the  dia- 
gram that  when  the  resistance  r 
of  the  bath  is  reduced  the  angle  <£ 
becomes  larger  and  the  power 
factor,  or  cos  </>,  consequently  de- 
creases. If  the  length  of  channel 
remains  the  same,  but  the  cross- 
section  of  the  bath  changes,  the  re- 
sistance will  change,  because  r  = 

p  —  and  as  the  example  showed, 


17HL 


FIG.  78. 


that  raising  the  charge  from  1350  kg.  (about  3000  Ib.)  to  1800 
kg.  (about  4000  Ib.),  that  is  about  33%;  and  as  the  cross- 
section  of  the  bath  increased  in  like  ratio,  it  becomes  ap- 
parent why  it  is  that  the  power  factor  falls  with  an  increasing 
metal  charge  in  the  bath. 

Beside  the  resistance  of  the  bath,  however,  the  coefficient 
of  self-induction  has  a  noteworthy  influence  on  the  size  of  the 
power  factor.  It  was  shown  in  Chapter  IV  that  the  coefficient 
of  self-induction  depends  upon  the  form  and  arrangement  of 
the  conductors.  In  order  to  give  the  reader  an  idea  of  this 
influence,  it  may  be  said  that  for  conductors  of  ring  form  having 
a  circular  cross-section,  the  following  formula  for  the  coefficient 
of  self-induction  holds  good: 


L  - 


.(4   log  nat-^- 


-  8).  10-9. 


Here  D  denotes  the  diameter  of  the  wire  coil,  and  d  the  diameter 
of  the  wire  itself. 

This  formula,  however,  is  only  strictly  correct  provided  the 
conductor  is  not  in  the  vicinity  of  any  good  magnetic  conductors. 


196  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

However,  it  follows  that  the  coefficient  of  self-induction  primarily 
depends  on  the  surface  surrounded  by  the  ring  formed  conductor, 
and  that  the  coefficient  of  self-induction  increases,  the  larger  the 
surface  becomes.  Besides  this  the  cross-section  of  the  conductor 
also  influences  this  factor,  and  as  the  formula  shows,  the  co- 
efficient of  self-induction  becomes  a  little  better  with  increasing 
cross-sections  of  the  conductor.  This  latter  influence,  however, 
is  too  small  to  nullify  the  lowering  of  the  power  factor,  occasioned 
by  the  "lowered  bath  resistance  when  the  cross-section  of  the 
bath  is  increased.  The  proof  of  this  is  plainly  seen  by  the 
examples  given. 

From  what  has  just  been  said  relative  to  the  power  factor 
it  is  apparent  what  the  active  causes  are,  and  why  Kjellin  and 
similar  furnaces  had  to  be  built  with  ever  decreasing  periodicities, 
for  increasing  capacities.  We  have  just  seen,  that  the  power 
factor  decreases  when  the  charge  is  increased,  due  to  the  lesser 
resistance  to  the  bath.  As  we  saw  in  Chapter  IV,  the  lowering 
of  the  power  factor  necessitates  a  greater  current  flow  than  it 
would  have  at  a  higher  power  factor,  in  case  the  furnace  is  to 
receive  the  same  power,  at  a  lower  power  factor  and  at  the  same 
voltage.  Heavier  currents,  however,  demand  an  increase  in  the 
copper  cross-section  of  the  primary  winding,  which  in  turn  in- 
creases the  needed  space  for  winding  the  coil.  To  this  must  be 
added  that  with  an  increased  capacity  the  energy  absorbed  by 
the  furnace  is  naturally  greater,  so  that  the  processes  to  be 
followed  may  not  be  unnecessarily  expensive.  This,  too, 
necessitates  the  use  of  a  larger  copper  conductor,  and  consequent- 
ly further  increases  the  winding  space.  With  the  same  thickness 
of  the  furnace  refractories,  this  can  only  take  place,  however, 
when  the  diameter  of  the  ring  shaped  hearth  is  increased;  and, 
as  we  saw  before,  this  causes  a  larger  coefficient  of  self-induction, 
and  with  it  a  further  decrease  in  the  power  factor.  With  an 
increasing  charge,  therefore,  the  power  factor  would  drop  very 
fast,  and  this  would  very  quickly  lead  to  impossible  operating 
conditions  with  the  frequency  remaining  the  same.  Fortunately 
by  lowering  the  frequency,  we  have  a  means  for  meeting  the 
lowering  power  factor.  In  order  to  recognize  this,  if  we  refer 


THE   KJELLIN  FURNACE 


197 


to  Fig.  78  again,  we  see  that  the  power  factor  is  determined  by 
the  equation  — 


as  r  and  L  are  given  by  the  bath  conditions,  it  is  only  possible  to 
influence  the  power  factor  by  altering  m,  and  the  power  factor 
will,  of  course,  be  larger,  and  so  much  better,  the  smaller  the 
quantity  m.  This  quantity  m  is  determined  by  the  equation 
m  =  2  TT  v  where  v  equals  the  number  of  cycles  per  second.  By 


15 


10.3 
10 


Gysinge 


VGleiwitz 

Gurtnellen 
kludno^v^^^  Volklingen 

^ 

0.4  1.1.5  2       3  3.8  4       5       6        7       8  8.5  9     10 

Tons  Capacity 

FIG.  79. 

lowering  the  periodicity,  the  quantity  m  is  reduced,  and  hence 
the  value  of  the  power  factor  is  kept  within  reasonable  limits 
for  any  particular  size  of  furnace.  Kjellin  also  availed  himself 
of  this  means,  and  the  curve  shown  by  Fig.  79,  which  appeared 
in  the  Elektrotechnische  Zeitschrift,  in  1907,  in  an  article 
by  Englehardt,  shows  under  what  conditions  the  lowering  of 
the  frequency  is  desirable,  with  Kjellin  furnaces  of  increasing 


198  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

size  actually  built  and  operated.  The  conditions  here  described 
are  also,  of  course,  more  or  less  applicable  for  every  other  induc- 
tion furnace  having  a  channel  hearth. 

It  is  well  to  mention  that  the  lowering  of  the  periodicity  is 
not  always  feasible  as  the  normal  frequencies  are  25,  50  or  60. 
It  is  not  possible  to  change  from  one  frequency  to  another  by 
means  of  stationary  transformers,  in  the  manner  employed  for 
voltage  transformations.  If  it  is  desired,  therefore,  to  connect 
to  an  existing  power  station  having  a  higher  frequency  than 
would  be  favorable  for  the  furnace  operation,  it  will  be  necessary 
to  employ  a  rotary  transformer.  In  addition  a  low  power  factor 
necessitates  comparatively  large  iron  cross-sections  in  the 
generator  as  well  as  in  the  transformer,  and  consequently  greater 
copper  lengths  for  the  windings,  making  a  more  expensive  in- 
stallation. In  order  to  give  an  idea  of  this,  we  may  say  that  a 
generator  of  25  cycles  only  costs  half  as  much  as  one  of  equal 
capacity  of  five  cycles. 

As  electrodes  are  avoided  with  Kjellin  and  other  induction 
furnaces,  the  regulating  apparatus  for  the  carbon  electrodes 
themselves  is  not  needed,  so  that  the  furnace  does  not  require 
any  movable  parts,  except  the  covers.  With  the  absence  of 
electrodes  there  are  consequently  no  electrode  losses,  which 
leads  us  to  the  efficiency  of  the  Kjellin  furnace.  As  the  furnace 
is  merely  a  specially  designed  transformer,  the  only  losses 
occurring  are  the  ones  usually  prevalent  in  ordinary  transformers. 
These  losses  are  due  to  the  iron  losses,  which  are  caused  by  the 
continually  changing  direction  of  the  magnetization,  and  the 
copper  losses  in  the  windings.  As  the  secondary  winding  in 
Kjellin  furnaces  is  solely  composed  of  the  metal  in  the  hearth, 
all  the  losses  which  ordinarily  appear  here,  are  used  instead  to 
advantage,  because  all  electrical  losses  manifest  themselves 
as  heat,  and  in  this  case  the  generation  of  heat  is  what  is  desired. 
Losses,  therefore,  can  only  occur  in  the  iron  core  and  in  the 
primary  coils.  The  purely  electrical  losses  of  the  induction 
furnace  transformer  hardly  exceed  those  of  the  ordinary  trans- 
former. On  the  whole,  the  electrical  efficiency  of  the  induction 
furnace  is  the  best  obtainable  in  any  electric  furnace.  As  a 


THE   KJELLIN  FURNACE 


199 


proof  of  the  highest  efficiency  of  induction  furnaces,  it  may  be 
said  that,  the  most  frictionless  transposition  of  electric  energy 
imaginable  into  heat  takes  place  here,  as  the  current  generated 
in  the  secondary  circuit,  i.e.,  the  induced  currents  in  the  iron 
bath,  are  generated  at  their  point  of  origin  and  directly  changed 
into  heat. 

Induction  furnaces  may,  therefore,  be  built  for  any  existing 
voltage,  for  to  generate  the  particularly  high  current  in  the 
bath  is  only  dependent  on  a  suitable  number  of  turns  in  the 
primary  winding.  It  was  pointed  out,  for  example,  that  the 
furnace  at  Gysinge,  having  a  capacity  of  about  1500  kg.  (3300 


FIG.  80. 

lb.),  is  operated  at  3000  volts,  its  primary  coil  is  arranged  with 
295  turns,  so  that  we  have  a  secondary  voltage  corresponding  to 

or  about  10  volts.     As  it  is  possible  to  use  any  existing  high 

potential  current  on  the  primary  side,  it  is  necessary  that  this 
part  be  shielded  against  coming  into  any  possible  contact  with 
other  conducting  material.  This  is  accomplished  by  completely 
encasing  the  furnace  transformer,  i.e.,  the  transformer  is  built 
with  a  protecting  shell,  so  that  contact  with  any  dangerous  parts 
during  the  operation  of  the  furnace  is  practically  impossible.  In 
addition  to  this  the  protective  covering  is  connected  with  a 
copper  conductor  to  the  earth,  or  grounded — so  that  in  case 
any  high  potential  current  should  strike  the  protective  shield, 
it  would  immediately  become  harmless  and  flow  to  earth.  Hence 


200  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

all  danger  to  those  operating  the  furnace  is  eliminated,  and  the 
best  proof  of  the  absolutely  safe  operation  of  the  furnace,  is  the 
fact  that  thus  far  no  operatives  of  induction  furnaces  have  been 
injured. 

As  the  operation  of  the  induction  furnace  is  usually  not 
easily  understood  for  non-electricians,  the  schematic  connections 
of  a  Kjellin  Induction  furnace  installation  are  shown  in  Fig.  80. 
In  this  figure  the  left  half  shows  the  electric  installation  at  the 
central  station,  and  the  other  side  the  actual  furnace  installation. 
The  heavy  lines  between  the  central  station  and  the  furnace 
indicate  the  main  high  potential  conductors.  This  high  tension 
current  is  measured  with  instruments,  by  interposing  so-called 
potential  and  current  transformers  between  them  and  the 
main  conductors  so  that  the  instruments  only  carry  low  voltage 
currents.  The  thin  full  lines  indicate  the  necessary  wiring  for 
this.  If  we  neglect  for  the  moment  the  dotted  lines,  we  see  that 
the  full  lines  of  the  circuit  in  the  central  station  as  well  as  at  the 
furnace  show  instruments  at  either  place,  consisting  of  an 
ammeter  A ,  a  wattmeter  B,  and  a  voltmeter  C,  which  must  be 
watched  during  the  operation  of  the  furnace.  D  indicates  the 
current  transformers  for  measuring  current,  and  E  the  potential 
transformers  for  measuring  the  voltage.  In  order  to  protect 
the  instruments,  the  fuses  F  are  inserted,  whereas  G  represents 
an  automatic  release,  which  cuts  out  the  main  current  when  it 
is  overloaded  and  thereby  protects  the  generator.  The  generator 
itself  is  shown  by  H.  At  the  furnace  we  see  M  which  designates 
the  sectors  on  which  copper  brushes  rub,  (similarly  to  those 
usually  used  on  a  motor.)  in  order  that  the  furnace  may  receive 
its  current  and  still  remain  in  its  tilted  position.  From  the 
contact  rails,  the  current  is  carried  to  the  primary  winding  N, 
in  well  insulated  conductors,  which  generate  the  induced  cur- 
rents in  the  channel  O,  whose  contents  simultaneously  act 
as  the  secondary  winding.  If  we  also  mention  the  switch 
P,  at  the  furnace,  which  permits  the  current  to  be  inter- 
rupted there,  we  have  referred  to  all  the  apparatus  of  the  oper- 
ating circuit. 

Of  great  importance  is  the  regulating  apparatus  of  an  electric 


THE  KJELLIN' FURNACE  201 

furnace,  which  permits  the  furnace  to  receive  much  or  little 
energy,  and  thereby  enables  the  furnace  to  be  operated  practical- 
ly. We  saw  previously  with  arc  furnaces,  that  besides  this 
apparatus,  automatic  regulators  were  also  necessary,  in  order 
to  smooth  out  the  current  fluctuations  occasioned  by  the  action 
of  electrodes,  and  to  keep  a  predetermined  and  constant  amount 
of  energy  at  the  furnace.  These  regulators  are  wholly  absent 
with  induction  furnaces,  as  sudden  power  fluctuations  with 
induction  furnaces  are  absolutely  precluded.  We  have,  there- 
fore, only  to  confine  ourselves  to  the  apparatus  which  is  necessary 
to  regulate  the  incoming  energy,  and  for  this  it  is  quite  sufficient 
to  alter  the  primary  voltage  of  the  furnace. 

In  order  to  easily  change  the  voltage  during  the  operation 
at  any  time,  a  handwheel  rheostat,  or  regulator  is  placed  at  the 
central  station,  as  well  as  at  the  furnace,  by  the  aid  of  which  the 
magnetizing  or  exciting  current  is  varied  at  the  alternator.  In 
Fig.  80,  /  represents  the  exciter  generator,  the  heavier  dotted 
lines  indicate  the  main  wiring  of  the  excitation  circuit,  and  the 
lighter  dotted  line  denotes  the  shunt  circuit  of  the  exciter  gen- 
erator or  exciter.  At  the  furnace  is  the  small  regulator  L,  by 
the  aid  of  -  which  the  field  of  the  exciter  is  regulated  with  a  very 
light  current,  whereas  the  regulating  resistance  K  enables  the 
main  current  of  the  exciter  to  be  changed.  In  this  way  it  is 
possible  to  regulate  the  voltage  at  the  central  station  as  well  as 
at  the  furnace,  and  in  order  to  keep  both  regulating  platforms 
in  communication  with  each  other,  it  is  usual  to  have  them 
connected  by  means  of  loud-speaking  telephones. 

After  this  discussion  of  typical  Kjellin  furnace  switching 
methods,  which  are  applicable  also  to  other  induction  furnaces 
having  special  generators,  we  may  turn  to  the  comparison  of 
the  Kjellin  furnace  with  the  ideal  furnace.  That  the  Kjellin 
furnace  requires  special  generators  more  than  any  other  furnace 
discussed  in  detail,  was  seen  when  discussing  the  influence  of 
the  power  factor;  this  is  the  reason  for  the  abnormal  frequencies, 
which,  up  till  now,  have  been  necessary  for  all  induction  furnaces 
having  only  the  ring-shaped  hearth.  The  operation  of  a  Kjellin 
furnace  with  other  than  its  own  special  generator,  is  not 


202  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


practicable  and  this  increases  the  installation  cost,  and  affects 
the  obvious  advantages  of  the  furnace. 

Among  the  special  advantages  of  the  Kjellin  furnace,  as 
the  typical  representative  of  the  pure  induction  furnaces,  we 
may  count  first  of  all  the  absolute  avoidance  of  any  sudden  or 
undesirable  power  fluctuations,  which  must  be  classified  as 
unavoidable  with  arc  furnaces  having  vertical  or  inclined  elec- 
trodes. That  there  are  no  reasons  for  these  sudden  power 
changes  with  Kjellin  furnaces  we  see  when  we  realize,  that  with 
this  pure  resistance  heating,  sudden  power  changes  could  only 


Wg't  Cont't  Prod. 


FIG.  81. 

occur,  with  sudden  heavy  cross-sectional  changes  of  the  bath. 
This  condition,  though,  is  positively  eliminated  because  the 
cross-section  can  only  vary  when  charging  or  when  tapping  the 
furnace,  and  as  these  operations  are  always  the  function  of  a 
greater  or  lesser  amount  of  time,  it  is  evident  that  cross-sectional 
changes  can  only  appear  gradually  during  this  time,  and  likewise 
the  resistance  changes  and  changes  the  current  strength.  This 
is  proved  from  the  operation  of  all  induction  furnaces.  There 
is,  however,  a  decided  advantage  in  avoiding  any  sudden  power 
changes,  for  it  is  evident  that  the  generator  required  for  an 
induction  furnace  needs  to  be  just  large  enough  to  carry  the 
maximum  load  required  over  a  period  of  time;  whereas  a  genera- 
tor for  an  arc  furnace  would  have  to  be  more  liberally  propor- 
tioned, considering  the  heavy  load  fluctuations.  The  curve 


THE   KJELLIN  FURNACE  203 

of  Fig.  57  shows  to  what  degree  these  power  fluctuations  occur, 
and  it  is  interesting  to  compare  this  with  the  one  shown  by 
Fig.  81,  which  latter  shows  a  Kjellin  furnace  under  various 
methods  of  operation.  These  conditions  naturally  tend  to 
cheapen  the  construction  of  the  generator  for  the  induction 
furnace,  so  that  the  greater  cost  occasioned  by  the  generator  of 
abnormal  periodicity  is  at  least  compensated  for  to  a  certain 
extent. 

It  was  seen  when  discussing  the  switching  mechanism,  that 
the  regulation  of  the  incoming  energy  of  a  K  jell  in  furnace  is 
accomplished  in  the  simplest  way  imaginable.  It  may,  therefore, 
be  well  to  point  out  again  that  the  regulation  of  the  energy  of 
an  induction  furnace  is  accomplished  in  the  most  ideal  way. 
For  with  an  electric  furnace,  the  same  temperature  is  found 
throughout  the  whole  bath,  so  that  any  change  of  the  incoming 
energy  alters  its  temperature  gradually  without  in  any  way 
causing  any  overheating  at  any  one  spot,  which  is  always  to  be 
dreaded  under  the  electrode  in  arc  furnaces. 

It  has  also  been  mentioned  that  the  induction  furnace  un- 
doubtedly has  the  best  attainable  electrical  efficiency  of  any 
electric  furnace,  because  all  electrode  losses  are  avoided,  and 
hence  only  the  transformer  losses  come  into  play  with  induction 
furnaces,  except  when  a  special  generator  is  used,  and  then  only 
the  primary  copper  losses  and  iron  losses  appear  in  the  trans- 
former parts  built  into  the  furnace.  Transformer  losses  are, 
however,  present  with  nearly  every  arc  furnace,  thus  a  transform- 
er is  almost  invariably  erected  as  closely  as  possible  to  the  furnace. 

As  the  Kjellin  furnace  today  is  always  built  of  the  tilting 
variety,  it  fulfills  one  more  demand  of  the  ideal  electric  steel 
furnace.  On  the  other  hand,  the  Kjellin  furnace  cannot  -fulfill  the 
demand  which  provides  for  an  easily  surveyed  and  accessible 
hearth  and  herein  lies  its  great  weakness  as  compared  with  other 
furnaces;  its  use  is  therefore  restricted  to  that  comparatively 
small  field,  in  which  the  requirement  of  an  easily  surveyed  and 
accessible  hearth  is  immaterial.  Such  occasions  may,  however, 
occur  where  a  furnace  is  intended  to  be  a  substitute  for  the 
crucible  furnace,  in  which  a  very  pure  material  is  mixed  in  the 


204   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

bath,  or  in  case  the  charge  from  other  furnaces  is  merely  to  stand 
in  the  electric.  The  Kjellin  furnace  or  any  other  induction 
furnace  with  a  ring-shaped  hearth,  is  found  preferable  to  be 
used  in  this  way.  The  advantage  it  has  over  the  crucible,  is 
that  much  larger  homogeneous  quantities  of  a  desired  quality 
can  be  obtained,  whereas  crucibles  always  have  a  very  limited 
capacity;  it  is,  difficult  therefore,  to  produce  large  amounts  of  a 
predetermined  and  regular  composition.  Furthermore,  the 
induction  only  needs  a  very  limited  number  of  operating  men. 


FIG.  82. 

Finally,  a  considerable  amount  of  money  can  be  saved  in  the 
crucibles  (from  $5  to  $8  in  regenerative  furnaces,  but  as  high  as 
$20  a  ton  in  non-regenerative  "pan  system  "  oil  burning  furnaces). 
As  a  substitute  for  the  above,  the  Kjellin  furnace  seems  admirably 
suited.  For  most  other  classes  of  work,  however,  the  furnace  is 
unsuitable;  because  it  is  practically  impossible  to  thoroughly 
remove  the  slag  from  the  ring- shaped  channel  hearth,  and  thus 
avoid  affecting  the  purifying  process  for  the  succeeding  slag. 
This  fact  has  been  proved  in  practical  work  by  many  and  ex- 
tensive tests. 

One  of  the  next  requirements  of  an  ideal  furnace  is  the 
adequate  circulation  of  the  bath  by  the  aid  of  which  the  furnace 
will  produce  a  thoroughly  regular  material.  On  account  of  the 
magnetic  conditions  of  the  Kjellin  furnace  the  circulation  of  the 
hearth  metal  is  almost  perfect.  The  proof  of  this  was  first 
published  by  Englehardt  in  The  Electrotechnische  Zeitschrift, 
in  1907,  and  is  shown  schematically  in  Fig.  82.  Here  0/  denotes 


THE   KJELLIN  FURNACE  205 

the  lines  of  force  generated  by  the  primary  coil,  which  take  their 
path  through  the  transformer  iron.  <£i"  denotes  those  which 
are  generated  by  the  secondary  winding  or  the  bath,  and  take  a 
path  through  the  transformer  iron  in  the  opposite  direction,  so 
that  we  have  resultant  lines  of  force,  denoted  by  <£.  On  account 
of  the  large  distance,  however,  between  the  primary  and  second- 
ary coils,  there  must  also  necessarily  be  a  number  of  stray  lines 
of  force,  which  find  their  path  through  the  air.  As  far  as  these 
are  generated  by  the  primary  winding,  they  are  designated  by 
<£/,  and  when  generated  by  the  currents  flowing  in  the  iron  bath, 
they  are  designated  by  <f>s".  These  lines  of  force  play  a  very 
important  part,  as  the  iron  and  the  molten  metal  offer  a  much 
lesser  resistance  to  the  lines  of  force  than  the  air  does,  so  that 
it  may  be  assumed  that  a  part  of  the  secondary  lines  of  force 
find  their  way  through  the  molten  metal.  Both  lines  of  force, 
<f>a'  and  <£s",  therefore,  essentially  flow  in  opposite  directions,  as 
they  are  generated  by  currents  having  opposite  directions.  (We 
saw  in  Chapter  IV  that  the  induced  current,  i.e.,  the  current  gen- 
erated by  induction,  is  always  in  the  opposite  direction  to  the  pri- 
mary current,  which  is  the  case  here.)  Fig.  82,  however,  shows  that 
the  opposite  direction  of  these  two  lines  of  force  circuits,  makes  the 
direction  of  current  flow  the  same  between  the  primary  winding 
and  the  bath.  It  is  a  fact  that  lines  of  force  of  the  same  direction 
repel  each  other,  hence  forces  must  appear  between  the  primary 
winding  and  the  bath,  which  endeavor  to  repel  the  molten  metal 
from  the  primary  coil  toward  the  outside.  In  Fig.  83  this  force 
is  denoted  by  Ps.  Besides  this  the  force  of  gravity  also  operates 
on  the  bath.  Both  forces  work  at  right  angles  to  each  other, 
causing  a  resultant  force.  Accordingly  the  surface  of  the  bath 
inclines  at  right  angles  to  this  resultant,  as  is  shown  in  Fig.  83. 

As  a  matter  of  fact  the  inclination  of  the  bath  surface  can  be 
more  or  less  plainly  seen  with  all  Kjellin  furnaces.1  The  flow  of 
the  metal  is  from  the  outside  upper  edge  towards  the  inner  lower 
one,  which  in  this  way  provides  an  intimate  mixing  of  the  metal 


1  The  inclination  of  the  bath  of  an  8-ton  Kjellin  furnace  is  about  24°  (See 
Stahl  und  Risen,  1910,  p.  1071). 


206  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


in  the  bath.  One  explanation  of  this  flowing  or  rolling  of  the 
bath  may  be  made,  if  we  assume  that  the  parts  lying  on  the  outer 
upper  edge  are  subject  to  a  greater  cooling  than  the  inside  lower 
lying  metal,  so  that  the  higher  lying,  cooler  and  consequently 
specifically  heavier  metal  portions  will  tend  to  sink  to  the  bottom, 
whereas  the  hot  portions  will  rise. 

The  circulation  described  has  the  advantage  of  the  most 
thorough  mixing  of  the  whole  furnace  contents  without  mechani- 
cal aid.  With  large  Kjellin  furnaces  operating  at  low  frequencies, 
however,  it  has  frequently  happened  that  the  inner  wall  of  the 


FIG.  83. 

refractories  is  quickly  destroyed  by  the  circulation  directed 
against  it.  It  was  only  after  decided  efforts  on  the  part  of  the 
Poldihiitte  at  Kladno,  Austria,  in  applying  the  refractories  in 
a  special  way  that  they  were  able  to  withstand  these  attacks,  so 
that  the  lining,  even  with  an  8-ton  Kjellin  furnace,  now  lasts  six 
weeks,  (164  heats,)  when  melting  cold  stock,1  and  494  heats 
with  hot  charges.2 

In  the  discussion  of  the  Kjellin  furnace  circulation,  it  must 
be  stated  that  the  pinch  effect  mentioned  in  Chapter  III  does 
not  come  into  play  as  long  as  the  furnace  is  used  for  melting  iron 
because  the  bath  cross-sections  in  relation  to  the  current  density 
are  too  large  when  this  furnace  is  thus  used.  The  pinch  effect 
could  only  be  found  if  the  cross-section  should  be  especially 
narrowed  at  particular  places. 

If  it  has  been  shown  that  the  Kjellin  furnace  is  only  a  sub- 
stitute for  the  crucible,  still  it  may  be  said  concerning  the  sizes 
this  furnace  has  attained,  that  at  present  the  Kjellin  furnace 

^See  also  Metallurgical  and  Chemical  Engineering,  February,  1913,  details  of 
Kladno  lining.  2  In  1919,  the  General  Electric  Co.,  of  New  York,  have  also 
brought  out  an  improved  bottom  and  lining  for  this  type  of  furnace. 


THE  KJELLIN  FURNACE 


207 


has  a  capacity  of  8  tons  of  steel.  One  of  these  furnaces  is  operat- 
ing successfully  at  the  works  of  Friedr.  Krupp,  at  Essen,  Germany. 
Fig.  84  shows  the  transformer  of  one  of  these  8-ton  Kjellin 
furnaces  for  only  five  cycles.  It  is  hardly  advisable  to  build 
Kjellin  furnaces  of  a  larger  size  than  this,  first  because  the  fre- 


FIG.  84. 

quency  would  have  to  be  reduced  still  further,  and  secondly, 
because  it  is  to  be  feared  that  there  would  be  difficulties  with 
the  durability  of  the  refractories. 

Regarding  the  total  efficiency  of  the  furnace,  we  append  the 
following: 

Several  reports  have  been  made  by  Englehardt  on  the 
Kjellin  furnaces.  In  Stahl  und  Risen,  1905,  page  205,  where 
he  speaks  of  melting  a  charge  consisting  of  1/3  pig  iron  and  2/3 
scrap,  he  figured  with  a  theoretical  power  consumption  of  489 
Kw.  hours  per  ton.  If  we  compare  the  results  obtained  with  the 
1.5-ton  Kjellin  furnace,  where  with  a  mixture  as  above  it  took 


208  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

966  Kw.  hours  to  melt  a  ton  of  steel  over  a  six-hour  melting 
period,  and  800  Kw.  hours  during  a  four-hour  period,  this 
gives  a  total  efficieijcy  of  50%  for  the  six-hour  melting  time, 
whereas  Kjellin  himself  mentions  47%,  and  an  efficiency  of  60% 
for  the  four-hour  melt.  It  is  interesting  to  observe  how  the 
shortened  melting  time  raises  the  attainable  efficiency  of  a 
furnace.  The  reason  for  this  is  that  on  one  hand,  the  radiation 
losses  are  prolonged  for  six  hours,  whereas  on  the  other  they  only 
occur  for  four  hours.  While  melting,  therefore,  it  is  advisable 
to  operate  with  as  high  an  incoming  energy  as  possible,  and  to 
hasten  the  work  to  the  greatest  extent.  The  60%  efficiency 
with  a  four-hour  charge  is  to  be  considered  as  most  favorable, 
considering  the  small  size  of  the  furnace  (itf  tons).  The 
attainment  of  such  efficiencies,  with  Kjellin  furnaces  having 
such  an  unfavorable  hearth,  as  far  as  radiation  losses  are  con- 
cerned, is  only  possible  because  the  electrical  losses  are  at  a 
minimum.  In  spite,  however,  of  the  assumed  greater  radiation 
losses  of  the  Kjellin  furnace  as  compared  with  the  arc  furnace, 
we  find  that  the  induction  furnace  always  has  a  higher  total 
efficiency  than  the  arc  furnace.  This  becomes  even  more  appar- 
ent with  larger  furnaces.  In  the  same  article  as  above,  Engle- 
hardt  gives  an  efficiency  of  an  8-ton  furnace  corresponding  to  a 
power  consumption  of  590  Kw.  hrs.,  when  melting  cold  stock. 
This  gives  a  total  efficiency  of  about  80%.  That  this  figure  is 
attainable  as  a  matter  of  fact  is  best  proven  by  the  practical 
operation,  where  with  this  ring-shaped  hearth  a  power  consump- 
tion of  only  580  Kw.  hrs.  per  ton  of  steel  was  attained  by  the  use 
of  suitable  heat  insulating  covers. 

Regarding  the  application  of  this  furnace,  we  refer  to  the 
statistics  in  the  closing  chapter. 

The  sale  of  and  giving  licenses  for  Kjellin  furnaces  is  handled 
by  the  Gesellschaft  fur  Elektrostahlanlagen  in  Berlin;  in  Eng- 
land and  her  colonies,  except  Canada,  by  the  Grondal-Kjellin 
Co.,  London,  and  in  the  United  States  and  Canada  formerly 
by  the  American  Electric  Furnace  Co.,  New  York,  and  at  pres- 
ent by  Naylor  &  Co.,  agents  for  Grondal-Kjellin  Co.,  New  York. 


CHAPTER  XIII 
THE  ROCHLING-RODENHAUSER  FURNACE 

ALTHOUGH  we  saw  in  the  previous  chapter  that  the  Kjellin 
furnace  and  the  induction  furnace  having  a  ring-shaped  hearth, 
are  inapplicable  for  many  uses,  and  hence  at  a  great  disadvantage 
with  the  arc  furnace,  still  the  induction  furnace  has  important 
advantages  which  must  not  be  overlooked,  especially  where  this 
furnace  in  its  original  form  finds  its  best  field;  viz.:  in  the  re- 
placement of  the  crucible  furnace.  These  advantages  include 
the  absence  of  electrodes,  and  consequent  saving  in  operating 
costs  and  also  the  avoidance  of  the  risk  of  accidental  impurities 
from  the  electrodes  contaminating  the  bath,  which  latter  is 
especially  feared  when  making  tool  steel.  The  electrical  effi- 
ciency attainable  is  also  much  higher.  The  absolutely  steady 
furnace  operation  is  almost  ideal,  and  this  steadiness  is  equally 
excellent  for  the  central  station.  Finally,  we  may  regard  the 
uniform  heating  effect  throughout  the  entire  bath  of  the  in- 
duction furnace  together  with  its  strong  circulation,  an  advan- 
tage over  the  arc  furnace,  even  though  the  experience  thus 
far  gained  concerning  the  influence  of  the  high  temperature  of 
the  arc  on  the  quality  of  the  steel  is  not  yet  extensive  enough 
to  form  a  conclusive  opinion  on  this  point. 

Realizing  the  good  points  of  the  induction  furnace  referred 
to  above,  it  was  not  long  before  efforts  were  made  to  retain  the 
advantages  of  induction  heating.  For  the  disadvantages  of  the 
single  ring  hearth  were  clearly  recognized.  Later  on  pains  were 
taken  to  alter  the  hearth  in  such  a  way  that  it  would  meet  the 
demands  of  the  metallurgist,  and  to  produce  thereby  an  induction 
furnace  which  would  be  equal  to  any  refining  work.  It  was 
recognized  that  if  at  the  same  time  the  operating  conditions 
could  be  bettered  (these  as  we  have  seen  with  the  Kjellin  furnace 


210  ELECTRIC  FURNACES  IN  THE  IRON   AND  STEEL  INDUSTRY 

necessitate  the  use  of  machines  having  unusual  periodicities), 
then  the  induction  furnace  would  be  able  to  enter  into  successful 
competition  with  the  arc  furnace  in  any  field. 

It  was  these  considerations  which  led  the  Rochling  Eisen 
und  Stahlwerke  at  Volklingen  on  the  Saar,  Germany,  to  consider 
the  problem  of  re-designing  the  induction  furnace.  This  de- 
cision was  reached  only  after  it  was  clearly  recognized  that  the 
single-ring  channel  induction  furnace  was  not  practical  for  refin- 
ing work. 

The  first  German  Rochling-Rodenhauser  patent  was  applied 
for  on  May  6,  1906,  and  subsequently  granted  (No.  199354  *). 


FIG.  85. 

This  patent  covers  an  induction  furnace  as  shown  schematically  in 
Fig.  85.  It  may  be  seen  that  both  cores  of  the  transformer  are 
provided  with  coils,  in  contradistinction  to  the  Kjellin  construc- 
tion. Both  cores  are  surrounded  by  an  induction  channel,  which 
are  joined  between  the  cores  in  the  middle,  forming  a  roomy  work- 
ing hearth.  This  middle  section  is  sometimes  heated  by  means 
of  an  auxiliary  current  supplied  by  a  secondary  winding  wound 
next  to  the  primary  winding,  which  has  the  marked  advantage 
of  reducing  the  stray  field,  and  hence  improves  the  power  factor. 

1  Corresponding  to  U.  S.  patent  No.  877739  of  Jan.  28,  1908. 


THE  ROCHLING-RODENHAUSER  FURNACE 


211 


The  furnace  principal  shown  in  the  sketch  is  known  as  the  Roch- 
ling-Rodenhauser  furnace.  This  furnace  was  investigated  for 
its  usefulness  at  the  Rochling  Iron  &  Steel  Works  from  July  to 
September,  1906,  by  means  of  a  small  test  furnace  holding  60 
kg.  (132  lb.),  and  operated  from  a  50  cycle  circuit.  Fig.  86  shows 
this  furnace  at  one  stage  of  the  tests  with  suspended  electrodes 
composed  partly  of  conductors  of  the  second  class,  being  used 
as  a  mode  of  utilizing  the  auxiliary  current,  notwithstanding 


FIG.  86. 

that  the  patent  specification  mentions  conductors  of  the  second 
class  for  transferring  the  current,  which  is  the  method  exclusively 
employed  today. 

The  tests  with  the  small  furnace  were  later  continued  with  a 
somewhat  larger  furnace,  holding  about  300  kg.  (660  lb.). 

In  the  course  of  the  development  a  furnace  of  about  500  to 
750  kg.  (noo  to  1650  lb.),  was  ordered  by  and  constructed  for 
the  Richer  Hiittenverein,  which  company  was  desirous  also  of 
investigating  this  form  of  furnace,  knowing  of  the  tests  carried 
out  at  Volklingen.  Until  this  time,  the  small  furnaces  were 


212    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

provided  with  covers  which  had  to  be  lifted  when  charging,  but 
the  Eicher  Hiittenverein  furnace  was  the  first  one  to  be  supplied 
with  doors,  thus  simplifying  the  furnace  operation.  This 
arrangement  may,  at  the  same  time,  serve  to  indicate  how,  with 
the  progress  of  developments,  the  work  of  refining  in  the  furnace 
was  transferred  more  and  more  from  the  channels  to  the  main 
hearth,  where  it  is  carried  on  today  exclusively,  the  channels 
serving  only  as  heat  carriers,  without  in  any  way  accomplishing 
any  metallurgical  work. 

One  of  the  determining  factors  in  the  further  development 
of  the  furnace  was  due  to  the  erection  in  the  spring  of  1907,  at 
Volklingen,  of  an  8-ton  Kjellin  furnace  which  operated  at  only 
five  cycles.  The  exhaustive  tests  carried  on  with  the  aid  of  this 
furnace,  furnished  convincing  proof  that  the  ring-shaped  hearth 
was  unsuitable  for  extensive  refining,  which  was  the  goal  of  the 
Rochling  Iron  &  Steel  Works.  On  the  other  hand,  these  small 
test  furnaces,  above  mentioned,  gave  the  most  favorable  results 
in  the  refining  of  steel.  Because  of  this  a  Rochling-Rodenhauser 
furnace  was  built  and  designed  for  the  electric  plant  which  had 
been  installed  to  operate  the  five-cycle  Kjellin  furnace.  This 
first  large  furnace  had  a  capacity  of  about  3  tons  and  was  placed 
in  operation  on  June  22,  1907.  It  soon  demonstrated  the  ad- 
vantages of  the  new  furnace  principle  for  large  units. 

In  order,  however,  to  render  this  furnace  system  adaptable 
to  all  conditions,  there  was  still  one  further  step  to  take,  i.e., 
to  derive  means  to  operate  the  furnace  with  polyphase  current. 
For  as  long  as  it  was  not  possible  to  use  polyphase  current 
directly  in  the  induction  furnace,  the  advantage  of  the  induction 
furnace  in  its  being  able  to  be  operated  with  any  voltage  that  is 
available,  would  be  of  minor  importance.  The  reason  for  this 
being  that  as  it  is  only  possible  to  operate  the  furnace  with  single 
phase  current,  it  follows  that  the  installation  of  a  rotary  trans- 
former would  be  necessary  when  obtaining  power  from  a  three- 
phase  circuit. 

As  early  as  1907,  therefore,  the  constructive  features  of  a 
polyphase  furnace  were  considered,  and  in  February,  1908,  the 
first  polyphase  Rochling-Rodenhauser  furnace  was  placed  in 


THE  ROCHLING-RODENHAUSER  FURNACE 


213 


FIG.   86a. — Two   Phase  R.-R.  In- 
duction Furnace. 


operation.  This  was  designed  for  50  cycles  and  connected  to  the 
3  phase  electric  plant  of  the  Rochling  Iron  &  Steel  Works.  The 
application  of  the  furnace  to  polyphase  current  was  patented  in 
all  industrial  countries. 

These  short  remarks  show  the  development  of  the  Rochling- 
Rodenhauser  furnace,  which  can  be  obtained  to-day  not  only  for 

single  phase  current,  but  also 
for  two  and  three  phase  cur- 
rent, for  any  convenient 
voltage  and  for  normal  fre- 
quencies. 

In  its  present  form  the 
Rochling  -  Rodenhauser  fur- 
nace consists  of  a  casing  of 
strong  sheet  iron,  which  is 
supported  by  means  of  a 
semi-circular  saddle  and  rack 
ori  rollers,  thus  allowing  the 
furnace  to  tilt.  The  tilting 

may  be  accomplished  in  any  way  desired,  but  is  usually  done 
by  means  of  an  electric  motor  and  suitable  gearing. 

The  furnace  transformer  is  built  into  the  shell.  The  upper 
yoke  of  the  transformer  is  arranged  to  be  easily  removable,  while 
the  lower  yoke  and  the  cores  are  securely  fastened  by  bolts,  to 
the  furnace  casing,  so  that  the  transformer  may  stay  securely  in 
position  even  though  the  furnace  is  tilted  45°.  If  we  now  turn 
to  the  furnace  in  its  single  phase  form  as  shown  in  Figs.  87  to 
89,  which  indicates  a  5 -ton  furnace  operating  at  15  cycles,  5000 
volts,  we  find  two  cores  of  somewhat  long-drawn-out  rectangular 
form.  The  cores  are  composed  of  a  number  of  sections,  which  in 
turn  are  built  up  of  paper-covered  sheet  iron  of  .3  mm.  (.012  inch) 
thickness,  the  sections  being  separated  from  each  other  by  the 
ventilating  ducts  H.  Each  core  carries  a  primary  winding  A, 
and  a  secondary  winding  B.  The  primary  winding  is  connected 
directly  to  the  incoming  voltage  intended  for  the  furnace,  in  the 
foregoing  case,  5000  volts.  The  current  is  led  to  the  windings 
by  means  of  the  usual  high  tension  underground  cable  and  thence 


214  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

to  brushes,  by  the  aid  of  which  it  is  carried  to  a  copper  slip  ring. 
The  current  is  then  led  directly  to  the  winding,  by  stationary 
conductors  carried  on  high  tension  insulators.  These  methods 
of  leading  the  current  to  the  windings  have  the  advantage  that 
the  heating  may  be  continued,  for  instance,  when  the  slag  is  being 
rabbled  off,  i.e.,  the  furnace  continues  to  receive  its  heat  when 
in  the  tilted  position.  The  secondary  winding  lies  next  to  and 


FIG.  87. 

separated  from  the  primary  winding  by  an  air  space,  which  is 
both  an  insulating  protection  and  a  cooling  chamber.  The 
secondary  winding  is  composed  of  heavy  copper  strips  and 
carries  very  heavy  currents  at  very  low  voltages.  From  this 
secondary  winding,  copper  connections  lead  upwards  from  which 
the  current  is  led  to  the  poleplates  E.  These  connecting  pieces 
are  represented  by  lines  in  Fig.  87. 

The  whole  winding  arrangement  is  surrounded  by  two 
cylinders  of  copper,  brass  or  monel  metal,  which  are  separated 
from  each  other  by  an  air  space.  Similarly  there  is  an  air  space 


THE  ROCHLING-RODENHAUSER  FURNACE 


215 


between  the  secondary  winding  and  the  inner  cylinder.  The 
inner  cylinder  is  closed  at  the  top  by  means  of  dust  catchers  in 
such  a  way,  however,  that  the  cooling  air  from  the  furnace  trans- 
former may  escape  at  the  upper  end  with  the  least  resistance. 
The  method  of  supplying  the  cooling  air  is  shown  by  means  of  the 
central  air  duct  in  Fig.  88,  and  the  air  direction  is  shown  by  the 
arrows.  As  a  matter  of  fact  this  represents  the  method  of 


FIG.  88. 

applying  the  air  supply  for  Rochling-Rodenhauser  furnaces 
today,  for  such  a  centrally  located  movable  duct  underneath  the 
furnace  is  provided  from  which  the  air  is  led  to  both  cores.  The 
air  is  so  divided  that  the  greater  part  takes  its  path  upward 
through  the  winding  space,  thereby  cooling  the  coils  and  the 
transformer  cores,  whereas  a  smaller  part  passes  through  the 
space  between  the  two  protective  cylinders  M ,  in  order  to  keep 
the  heat  radiating  from  the  brickwork,  away  from  the  whole 
transformer  construction. 

Air  is  alone  used  for  cooling  from  a  blower  usually  of  very 


216   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

low  pressure.  At  Volklingen  for  instance  with  an  8-ton  single 
phase  furnace  the  blower  pressure  only  corresponds  to  40  mm. 
(1.6  inches)  water  gauge  pressure.  These  cooling  arrangements 
have  given  the  most  complete  safety  to  the  furnace  during  the 
past  8  years'  continuous  operation. 

In  order  that  the  unavoidable  cooling  of  the  furnace  trans* 
former  may  not  cause  too  great  heating  losses,  much  considera- 


A I 


FIG.  89. 

tion  was  given  to  the  best  possible  heat  protection  for  the  hearth. 
On  that  account  the  outer  protective  cylinders  are  surrounded 
with  a  layer  of  granular  material,  which  acts  as  a  heat  protector. 
On  the  outside  of  this  follows  the  real  refractory  mass  of  either 
dolomite  and  tar  or  magnesite  and  tar.  In  order  to  obtain  a 
hearth  of  the  desired  shape  as  shown  in  the  figure,  a  wooden  or 
cast  iron  templet  is  lowered  into  the  furnace  after  the  bottom 
has  been  rammed  in,  in  a  similar  manner  as  with  the  Kjellin 
furnace.  On  the  side  of  this  templet,  the  hearth  walls  are 
tamped  in,  which  when  the  templet  has  been  removed  leaves 
the  necessary  space  for  the  molten  metal.  The  cross-section 


THE   ROCHLING-RODENHAUSER  FURNACE  217 

a  b  of  Fig.  87  plainly  shows  that  the  hearth  really  has  the  shape 
of  an  8.  It  may  be  seen  that  the  transformer  cores  are  sur- 
rounded on  the  outside  by  the  narrow  channels  C,  while  between 
the  cores  lies  the  true  hearth  and  working  chamber.  Working 
doors  are  provided  at  both  ends  of  the  hearth,  which  makes  this 
easily  accessible  and  hence  greatly  lessens  the  necessary  attend- 
ance at  the  furnace,  as  the  entire  roof  of  the  furnace  covering 
both  hearth  and  channels  remains  stationary  throughout  the 
whole  working  period.  The  channels  themselves  are  not  intended 
for  the  metallurgical  process,  but  they  are  of  course  necessary 
to  provide  the  induced  heating  currents  for  the  hearth. 

Concerning  the  hearth  refractories,  it  may  be  mentioned 
that  following  the  dolomite  and  tar  outer  hearth  walls,  there 
is  provided  a  layer  of  coarse-grained  heat  insulating  material, 
and  that  finally  between  this  and  the  furnace  shell  is  placed  a 
ring  of  heat  protecting  brickwork.  All  parts  of  the  roof  covering 
are  easily  removable,  in  order  that  they  may  be  easily  lifted  off 
and  quickly  replaced,  in  case  a  new  lining  is  to  be  rammed  in. 

It  was  remarked  before  that  the  copper  secondary  winding 
B  leads  to  the  poleplates  E.  These  plates  are  imbedded  in  the 
lining,  as  shown  in  Figs.  87  and  89.  They  are  made  of  soft  cast 
steel,  and  have  the  largest  possible  surface  on  the  side  toward 
the  hearth.  Between  the  poleplates  and  the  bath  is  the  hearth 
wall,  which  as  we  have  seen  consists  of  dolomite  or  magnesite  and 
tar,  so  that  the  poleplate  is  protected  against  direct  contact 
with  the  molten  metal.1 

Mention  has  been  made  in  previous  chapters  that  the  refrac- 
tories used  are  conductors  of  the  second  class.  That  is  to  say, 
these  materials,  which  are  non-conductors  at  low  temperatures, 
lose  their  resistance  more  and  more  with  increasing  temperatures, 
until  finally  they  become  comparatively  good  conductors  at 
the  temperatures  which  are  prevalent  in  electric  furnaces.  This 
property  of  conductors  of  the  second  class  is  sometimes  util- 
ized in  Rochling-Rodenhauser  furnaces  to  carry  the  current 
from  the  secondary  winding  by  means  of  the  poleplates  to  the 
molten  bath  itself.  In  this  manner  that  portion  of  the  lining 

1  See  "  The  Practicability  of  the  Induction  Furnace  for  the  Making  of  Steel 
for  Castings."  By  C.  H.  Vom  Baur.  American  Foundrymen's  Association. 
Vol.  XX,  1912. 


218   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


FIGS.  90  and  91. 


THE  ROCHLING-RODENHAUSER  FURNACE 


219 


over  the  poleplate  may  be  designated  as  the  mass  which  transfers 
or  conducts  the  current. 

At  the  beginning  of  the  furnace  heating  this  mass  will  act 
as  a  large  resistance  in  the  secondary  circuit.  This  holds  true 
as  long  as  the  furnace  is  heated  up  with  iron  rings,  exactly  as 
is  done  with  KjelJin  furnaces,  and  the  same  conditions  exist 
when  the  furnace  is  charged  with  its  first  hot  metal,  so  that  at 
first  we  only  have  simple  induction  heating.  As  the  furnace  is 
further  heated,  the  temperature  also  rises  in  the  conductor  of 


FIG.  92. 

the  second  class  in  front  of  the  poleplate,  and  the  resistance 
consequently  drops  under  correct  conditions,  the  secondary 
winding  soon  carries  a  considerable  portion  of  the  total  energy 
of  the  furnace  to  the  bath.  With  the  8-ton  furnace  at  Volklingen, 
this  result  usually  takes  place  in  twelve  hours. 

For  the  normal  operation  of  the  furnace  there  is  therefore 
a  double  heating;  first,  we  have  the  single  induction  heating 
in  which  case  the  ring  formed  parts  of  the  hearth  are  to  be 
designated  as  secondary  circuits,  and  secondly  the  heating  from 


220    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  current  of  the  copper  coil  secondary  winding,  which  is  carried 
to  the  bath  via  the  poleplates  and  conductive  lining.  The 
arrows  in  Fig.  87  show  both  current  plates  of  the  secondary  side, 
which  plainly  show  that  the  total  current  flows  in  the  same 
direction  through  the  hearth. 

The  conditions  are  much  the  same  in  three  phase  furnaces. 
These  furnaces  receive  the  three  conductors  from  the  three  phase 
circuit  on  three  cores,  which  are  very  similar  to  the  ones  of  the 
single  phase  furnace,  in  that  each  core  carries  a  primary  and  a 
secondary  winding.  Here  also  we  find  the  coils  surrounded  with 
an  inner  and  outer  protecting  cylinder,  through  which  the 
ventilating  air  flows.  In  building  these  furnaces,  it  was  the 
endeavor,  of  course,  to  provide  a  single  roomy  hearth,  which 
could  be  easily  surveyed  and  be  easily  accessible.  Following 
these  maxims  the  designs  shown  by  Figs.  90  to  92  were  evolved. 
The  central  hearth  is  consequently  surrounded  on  three  sides  by 
the  cores.  Toward  the  outside,  (corresponding  to  the  arrange- 
ment of  the  single  phase  furnace,)  these  are  encompassed  about 
by  induction  channels,  which  join  together  and  form  the  central 
hearth  A .  The  yoke  is  often  bent  around  in  the  form  of  a  horse- 
shoe, by  the  aid  of  which  the  cores  are  connected  at  top  and 
bottom. 

In  order  to  make  the  hearth  easily  accessible  and  visible  a 
door  is  fitted  between  each  two  cores,  of  which  the  one  opposite 
the  central  cores  is  supplied  with  the  tapping  spout.  The  furnace 
is  therefore  emptied  in  that  direction.  There  is  a  poleplate 
having  two  arms  near  each  door  toward  the  bath,  which  is  pro- 
tected by  the  conductive  lining  from  the  bath,  as  in  the  single 
phase  furnace.  The  arms  of  the  poleplates  are  connected  with 
one  pole  of  the  secondary  copper  winding,  whereas  the  free  ends 
of  the  other  pole  are  connected  together  to  the  neutral  point  N, 
by  means  of  the  copper  bar  connections  there  shown. 

In  order  that  there  shall  be  no  misconception  about  the 
current  connections  of  a  Rochling-Rodenhauser  furnace  Fig. 
93  is  given  which  shows  the  schematic  diagram  of  a  single  phase. 
Similarly  Fig.  94  shows  the  schematic  diagram  of  a  three  phase 
furnace. 


THE   ROCHLING-RODENHAUSER  FURNACE 


221 


In  Fig.  93  both  primary  coils  of  the  single  phase  furnace 
are  shown  connected  in  parallel.  This  also  applies  to  the 
secondary  coils,  which  are  connected  in  parallel  by  the  poleplates, 
between  which  the  current  flows  through  the  bath.  Fig.  94 
shows  the  primary  winding  for  a  three  phase  furnace  and  their 
neutral  point  A7 1 .  The  heavier  drawn  secondary  winding  of  the 
three  cores  has  one  end  of  each  coil  connected  to  the  neutral 
point  N  2,  while  the  free  ends  are  also  here  connected  to  the  pole- 


Fro.  93. 

plates,  between  which  the  current-carrying  lining  and  the  bath 
are  connected  as  heat-resisting  material.  Besides  this  both 
figures  show  the  hearth  and  channel  limits.  The  conduits  of  a 
channel  and  hearth  form  a  short  circuited  secondary,  in  which 
the  heating  currents  are  directly  induced. 

The  operating  method  resembles  that  of  the  open- hearth 
furnace,  as  a  roomy  working  hearth  is  provided,  and  hence  the 
conditions  are  present  for  successful  refining  work.  If  the 
furnaces  are  to  be  heated  up,  and  hot  metal  is  obtainable,  this 
heating  is  accomplished  similarly  to  the  method  used  with 


222   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Kjellin  furnaces,  i.e.,  iron  rings  for  starting  are  laid  in  the  furnace 
channels  before  the  roof  is  replaced,  which  rings  serve  to  bring 
the  lining  to  a  red  heat  under  the  action  of  the  induced  currents. 
When  this  is  accomplished,  hot  metal  is  taken  from  any  con- 
venient melting  furnace  and  charged  in  the  electric  furnace  -  and 
with  this  charging  the  starting  or  heat  rings  are  melted,  which 


FIG.  94- 

permits  a  quicker  heating  up  of  the  furnace,  as  the  cross-section 
is  larger  and  consequently  the  energy  supplied  is  greater.  This 
heating  permits  the  furnace  to  be  placed  in  operation  in  the 
shortest  time.  It  has,  however,  the  disadvantage  that  it  neces- 
sitates the  use  of  molten  metal  from  some  other  melting  furnace. 
Such  apparatus  is  often  available  and  the  molten  metal  may  be 
obtained  from  converters,  open-hearth  furnaces,  cupolas,  crucible 
pots  or  even  blast  furnaces,  so  that  the  disadvantage  is  seldom 
felt.  It  is  more  difficult,  when  a  source  of  molten  metal  is  not 
available,  to  start  the  electric  furnace,  and  a  melting  furnace 


THE  ROCHLING-RODENHAUSER  FURNACE 


223 


would  therefore  have  to  be  furnished  just  for  this  purpose.  In 
order  to  avoid  this  disadvantage,  trials  were  made  at  the  works 
of  the  Rochling  Iron  &  Steel  Co.,  with  the  object  of  starting  up 
induction  furnaces  without  the  use  of  molten  metal.  This  test 
produced  satisfactory  results,  and  the  method  is  patented. 

In  accordance  with  this  method,  the  starting  rings  are  solidly 
packed  with  pieces  of  scrap,  steel  turnings,  etc.,  until  the  heating 
channels  and  the  hearth  are  completely  filled.  After  the  roof  is 
replaced,  the  current  is  switched  on,  and  the  heating  rings  soon 
become  red  hot  under  the  action  of  the  current.  This  assumes 
that  with  the  furnace  voltage  remaining  the  same,  the  absorption 
of  energy  will  rise.  With  a 
2-ton  furnace  it  is  pos- 
sible, for  instance,  in  twelve 
hours,  to  render  the  entire 
furnace  contents  fluid,  and 
the  normal  operation  may 
then  start.  When  heating 
up  with  hot  metal  about 
eight  hours  would  be  neces- 
sary in  order  to  proceed 
with  the  normal  furnace 
operation. 

A   normal    heat  with  a 
Rochling-Rodenhauser    fur- 
nace is  much  the   same  as 
with    an    arc    furnace.     The 
first,  after  which  the  slag   is 


FIG.  95. 


dephosphorizing  usually  occurs 
completely  rabbled  off.  so  that 
no  deleterious  material  remains  to  delay  the  formation  of  the 
new  slag  for  desulphurization.  The  removal  of  the  slag 
occurs  by  rabbling  through  the  doors.  Of  course  it  is  im- 
possible to  remove  the  slag  from  the  channels,  where  they  sur- 
round the  cores,  as  these  channels  are  quite  unsuitable  for  this 
work.  On  this  account  they  are  permanently  closed  in  by  the 
furnace  roof,  as  is  the  hearth  itself.  As  the  slag  cannot  be 
removed  from  the  channels  some  provision  must  be  made  so 
that  the  slag  is  prevented  from  entering  the  channels.  This  is 


224  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


now  accomplished  by  placing  fire-resisting  bricks  of  magnesite 
or  dolomite  across  the  commencement  of  the  channels  in  such  a 
way  that  the  iron  bath  in  the  hearth  is  i  or  2  cm.  (3/8"  to  %"") 
higher  than  the  lower  edge  of  the  channel  bridging  bricks.  In 
order  to  avoid  as  much  as  possible  the  heat  losses  occasioned 
by  the  bridging  channel  bricks  coming  into  direct  contact  with 
the  metal  bath,  a  further  normal  roof  of  ordinary  fire-brick  is 
placed  over  them,  which  helps  to  lessen  the  heat  losses  by  en- 
training a  stationary  layer  of  air.  Fig.  95  shows  these  channel  bridg- 
ing bricks,  together  with  the  refractories  surrounding  the  channel. 
Mention  should  be  made  of  the  behavior  of  the  Rochling- 
Rodenhauser  furnaces  when  melting  down  scrap.  So  far  it  has 
not  been  possible  to  avoid  the  necessity  of  having  in  the  furnace 


FIG.  96. 

a  portion  of  the  charge,  which,  as  we  have  seen  with  the  Kjellin 
furnace  also,  is  necessary  when  working  up  scrap,  in  order  to 
provide  the  necessary  circuit  for  the  induced  current,  so  that 
the  scrap  charged  in  the  furnace  may  be  melted  down  under  the 
influence  of  the  electric  heating  currents  induced  in  the  remaining 
portion  of  the  previous  charge.  When  scrap  is  to  be  melted 
down,  therefore,  and  no  fluid  charge  is  at  hand,  the  disadvantage 
consists  in  not  being  able  to  pour  the  entire  charge.  A  certain 
percentage,  say  a  quarter  or  a  third  of  the  entire  contents,  must 
remain  in  the  furnace.  The  conditions  are  of  course  different 
when  operating  partly  with  a  fluid  charge,  as  for  instance  from 


THE  ROCHLING-RODENHAUSER  FURNACE 


225 


a  converter  or  an  open-hearth  furnace  and  partly  with  scrap. 
Then  the  conditions  are  similar  to  working  only  with  a  hot  charge, 
so  that  there  is  no  reason  for  leaving  any  of  the  charge  in  the 
furnace.  With  a  mixed  charge,  therefore,  the  metal  is  fully 
teemed  after  each  heat,  after  which  some  fluid  metal  is  taken 
from  some  other  furnace  and  poured  into  the  electric  furnace, 
which  permits  of  the  flow  of  the  induced  current.  Thereupon 
the  metal  to  be  melted  is  charged  gradually  or  at  once,  to  such  a 
degree  that  the  cold  and  hot  furnace  contents  at  times  reaches 
the  roof.  After  this  no  attention  is  necessary  until  the  entire 
contents  is  melted  down.  This  takes  place  without  the  slight- 
est current  disturbance,  while  the  current  and  kilowatt  curves 
rise  slowly,  as  shown  by  the  curves  in  Figs.  96  and  97,  which 


FIG.  97. 


were  taken  from  an  8-ton  single  phase  furnace,  and  from  a 
i. 5-ton  three  phase  furnace,  respectively,  both  at  Volklingen. 
In  the  latter  curve  it  is  to  be  noticed  that  one  division  denotes 
45  amperes,  also  50  volts,  also  30  kw.,  also  .1  for  the  power 
factor,  and  ten  minutes.  The  crosses  on  the  bottom  line  denote 
that  100  kg.  of  scrap  were  charged. 

It  is  also  of  importance  from  the  standpoint  of  the  practical 
operation  of  a  furnace  system  that  it  is  convenient  to  shut  down 
the  furnace  for  a  limited  time,  for  instance  over  Sunday.  During 
such  stops,  a  Rochling-Rodenhauser  furnace  is  partly  charged 
or  even  filled  to  capacity.  It  is  then  sealed  up,  after  which  the 
current  is  switched  off  and  the  furnace  requires  no  further  atten- 
tion. When  it  is  desired  to  start  up  again,  the  current  is  switched 
on  for  several  hours,  and  the  furnace  is  thus  heated  up  anew. 


226     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

When  starting  up  in  this  way  with  the  furnace  fully  charged,  the 
8-ton  furnace  at  Volklingen  after  a  2o-hour  shut-down  is  ready 
for  normal  operation  in  about  six  hours. 

The  method  of  operation  of  the  electric  furnace  is  exactly 
the  same  as  with  the  Kjellin  furnace,  as  far  as  the  induction 
heating  is  concerned,  which  is  generated  by  means  of  the  primary 
coil,  in  the  ring-shaped  portion  of  the  iron  bath.  This  is  applied 
in  Rochling-Rodenhauser  furnaces,  twice  on  single  phase,  twice  on 
two  phase,  see  Fig.  loia,  and  three  times  on  three  phase  furnaces. 
This  heating  therefore  does  not  require  any  further  explanation. 
On  the  other  hand  it  is  different  with  the  secondary  circuit, 
which  is  composed  of  the  copper  winding  wound  directly  over 
the  primary  coil.  The  current  then  flows  through  the  pole- 
plates,  the  current-carrying  lining,  and  the  metallic  bath. 

The  object  of  the  secondary  circuit  is  to  raise  the  power 
factor,  and  to  aid  the  heating  of  the  furnace  contents.  It  was 
seen  that  the  low  power  factor  of  the  Kjellin  furnace,  especially 
the  low  power  factor  of  the  larger  sizes,  led  to  the  use  of  machines 
having  very  low  frequencies,  which  materially  increased  the  cost 
of  installation.  The  reason  for  this  decreasing  power  factor  is 
found  in  the  low  bath  resistance,  together  with  the  high  coefficient 
of  self  induction,  which  was  caused  by  the  great  distance  between 
the  coil  and  the  bath.  It  was  therefore  necessary  to  investigate 
these  causes,  if  the  above-mentioned  lowering  of  the  power  factor 
was  to  be  avoided. 

In  order  to  increase  the  bath  resistance  the  long  rectangular 
form  of  core  was  chosen,  in  place  of  the  more  circular  shape  used 
with  the  Kjellin  furnace.  Furthermore,  by  placing  the  winding 
on  two  or  three  cores,  it  became  possible  to  materially  decrease 
the  inner  periphery  of  the  induced  part  of  the  bath,  as  compared 
to  that  of  the  Kjellin  furnace.  This  brought  about  substantial 
advantages,  so  that  the  power  factor  with  Rochling-Rodenhauser 
furnaces  stays  much  higher  than  with  Kjellin  furnaces  having 
equal  capacities  and  equal  frequencies,  even  during  the  heating 
up  period,  i.e.,  at  a  time  when  the  poleplate  circuits  cannot  yet 
do  much  work,  because  the  current-carrying  lining  has  too  high 
a  resistance.  In  order  to  further  decrease  the  leakage  as  much 


THE  ROCHLING-RODENHAUSER  FURNACE  227 

as  possible,  because  of  the  comparatively  large  distance  between 
the  primary  coil  and  the  bath  still  remaining,  use  was  made  of 
electric  conductors  placed  in  the  path  of  the  stray  lines  of  force. 
This  expedient  was  mentioned  when  discussing  induction  furnaces 
in  general. 

The  conductors  of  Rochling-Rodenhauser  furnaces,  which  ar<s 
placed  in  the  path  of  the  magnetic  leakage  lines,  are  used  there- 
tore  as  secondary  copper  coils,  so  that  the  currents  produced 
by  lowering  the  leakage  field  are  used  at  the  same  time  to  heat 
the  metal  bath.  The  influence  of  this  secondary  coil  is  most 
important,  and  can  best  be  shown  by  the  fact  that  with  the  i%- 
ton,  three  phase,  50  cycle  furnace  operating  at  Volklingen,  the 
power  factor  rose  from  0.5%  at  the  start  to  .8%  and  above,  as 
the  work  of  the  pole  plates  increased.  The  secondary  winding 
meanwhile  takes  up  from  20%  to  a  maximum  of  30%  of  the 
total  work  of  the  furnace. 

By  using  the  above  expedients,  which  consist  of,  ist-the 
bath  resistance  being  increased  within  practicable  possible  limits, 
2nd — the  coils  being  wound  on  two  or  three  cores,  and  3rd — the 
secondary  copper  coils  used  to  reduce  the  leakage  field,  it  is 
possible  to  build  Rochling-Rodenhauser  furnaces  for  standard 
frequencies,  viz.,  25  (50  in  Europe)  arid,  in  the  case  of  very 
large  units,  for  15  cycles  without  the  power  factor  falling  below 
values  found  elsewhere.  Polyphase  furnaces  of  3^2  tons  and 
50  cycles  are  quite  practical,  whereas  large  sizes  up  to  a  maximum 
of  15  tons  would  have  to  be  operated  with  15  cycles,  with  poly- 
phase current. 

With  the  given  conditions  in  the  secondary  circuit  of  the 
Rochling-Rodenhauser  furnace,  the  conductor  of  the  second 
class,  which  is  placed  in  front  of  the  poleplates  must  be  made  to 
conduct  as  soon  as  possible.  This  is  accomplished  primarily  by- 
giving  the  conductor  as  large  a  cross-section  as  possible,  and 
making  the  current  path  as  short  as  possible,  so  that  the  operation 
proceeds  only  with  very  low  current  densities.  In  order,  how- 
ever, to  force  a  current  passage,  and  thereby  provide  as  quick  a 
heating  up  as  possible,  with  the  comparatively  high  resistance 
of  the  conductor  of  the  second  class,  a  higher  voltage  is  used 


228  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

in  the  secondary  circuit  during  the  heating  up  period,  than  later, 
during  the  regular  operation.  A  convenient  expedient  for 
accomplishing  this  is  to  alter  the  number  of  turns  of  the  secondary 
winding;  this  may  be  accomplished  by  the  use  of  a  single  throw- 
over  switch.  In  this  way,  for  instance,  the  8-ton  furnace  at 
Volklingen  is  operated  with  20  volts  in  the  secondary  circuit, 
during  the  heating  up  period,  with  the  primary  voltage  remaining 
the  same,  whereas,  subsequently,  i.e.,  during  the  normal  operation 
only,  10  volts  is  used.  With  this  voltage  it  is  possible  to  conduct 
several  thousand  amperes  through  the  current-carrying  lining 
into  the  molten  metal.  This  naturally  brings  with  it  an  increased 
heating  effect,  even  though  the  main  heating  is  accomplished 
with  the  currents  directly  induced  in  the  bath;  also,  during 
normal  operation  the  current  encounters  a  resistance  in  its  path, 
in  the  current-carrying  mass  leading  to  the  bath,  similar  to  the 
resistance  mentioned  with  carbon  electrodes  in  arc  furnaces. 
In  accordance  with  this,  considerable  portion  of  the  energy 
generated  in  the  secondary  coil  must  necessarily  be  converted 
into  heat  in  the  current-carrying  lining.  This  would,  of  course, 
mean  substantial  losses,  provided  this  heat  could  not  be  utilized 
in  the  bath.  This  heat  is  however  utilized  as  the  metal  bath  is 
in  contact  with  the  current-carrying  lining,  which  may  be  re- 
garded merely  as  a  heat  resistor,  the  object  being  of  transferring 
the  heat  generated  in  it  to  the  bath.  Slight  radiation  losses  only 
occur  as  a  small  percentage  in  the  arms  of  the  poleplates, 
(which  however  possess  no  cooling  arrangements),  but  there 
are  no  appreciable  losses  otherwise,  excepting  those  which  for 
instance  are  occasioned  by  the  radiation  and  heat  conduction 
of  the  insulated  heating  channels,  as  already  described. 

Considering  the  foregoing,  we  may  regard  the  Rochling- 
Rodenhauser  furnace  as  a  combination  of  a  pure  induction 
furnace  with  a  pure  resistance  furnace,  so  that  the  usual  designa- 
tion of  the  furnace  as  a  "combination"  furnace  is  well  founded. 

If  the  combination  furnace  be  now  compared  with  the  ideal 
furnace,  it  may  be  said  concerning  the  utilization  of  every  available 
form  of  alternating  current,  that  the  furnaces  fulfil  this  require- 
ment to  a  considerable  extent,  for  they  may  be  built  for  any 


THE   ROCHLING-RODENHAUSER   FURNACE 


229 


prevailing  voltage  for  either  single  or  polyphase.  A  certain 
restriction,  however,  appears,  in  that  the  falling  power  factor 
with  increasing  size  furnaces  cannot  be  avoided,  even  though 
it  is  considerably  less  than  with  the  Kjellin  furnace.  Single 
phase  furnaces  of  3-  to  5-ton  capacities  are  practical  only  for  25 
cycles  and  less;  with  greater  capacities  they  can  only  be  built 
for  15  cycles.  With  polyphase  furnaces  the  drop  is  not  so 
sensitive,  so  that  here  3-ton  furnaces  may  be  built  for  50  cycles, 
and  i5-ton  furnaces  may  still  be  built  for  15  cycles. 

From  what  has  gone  before,  it  is  evident  that  sudden  power 
fluctuations  with  Rochling-Rodenhauser  furnaces  are  absolutely 
absent.     Where   value   is  placed   on  machinery  having  small 
repairs   and    long   life,  these 
furnaces  accordingly  mean  an 
ideal    load    for    the    central 
power  plant.    This  is  also  the     0 
case  when   it  is  necessary  to 
change    the    energy  supplied 
to  the  furnace,  and  thus  raise 
the  temperature  to  the  degree 
necessary  for  favorable  oper- 


ation    of    the    metallurgical  FIG.  98. 

process.     If  the  furnace  is  to 

operate  in  conjunction  with  its  own  generator,  it  can  best  be 
regulated  as  shown  by  the  wiring  of  Fig.  80  which  is  perfectly 
applicable  to  the  single  phase  Rochling-Rodenhauser  furnace. 
This  method  was  originally  applied  at  the  Rochling  works,  to 
an  8-ton  Kjellin  furnace,  and  is  used  unchanged  today  for  a 
furnace  of  the  same  size.  In  using  this  scheme  it  is  assumed 
that  the  generator  is  to  be  used  only  for  the  furnace.  As  it  has 
been  shown  that  the  combination  furnaces  have  the  advantage 
that  they  may  be  connected  directly  to  existing  polyphase  cir- 
cuits of  any  voltage  and  frequency,  even  for  furnaces  of  con- 
siderable size,  this  arrangement  becomes  particularly  interesting. 
For  instance  the  arrangement  may  be  used  at  all  works  which  do 
not  desire  to  erect  their  own  power  plant,  but  wish  to  use  current 
from  a  distant  central  station.  It  is,  however,  significant  for 


230     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

works  which  desire  to  form  a  definite  and  practical  opinion  of 
the  working  operation  of  the  Rochling-Rodenhauser  furnaces 
to  do  so  by  means  of  a  small  trial  installation.  Such  works 
would  lay  the  greatest  stress  on  the  ability  to  utilize  their  existing 
power  plant  in  order  to  reduce  the  initial  cost  of  a  trial  installa- 
tion. 

In  such  cases  it  is  necessary  to  regulate  the  voltage  at  the 
furnace  without  appreciably  disturbing  the  voltage  of  the 
central  power  plant.  This  is  accomplished  by  the  use  of  so- 
called  regulating  or  auto-transformers.  Fig.  98  shows  the  wiring 
scheme  for  one  of  these  for  three  phase  currents.  If  at  the 
points,  di,  a2,  and  a3,  for  instance,  a  certain  star  connected 
potential  of,  say,  500  volts  is  connected,  corresponding  to  a  phase 
voltage  of  289  volts,  and  if  there  are  289  turns  between  the 
neutral  point  and  a,,  a2,  and  a3,  then  there  are  only  260  turns 
lying  between  the  neutral  point  and  the  points  b,,  b2,  and  b3, 
there  will  be  only  a  260  phase  voltage  between  these  points  and 
the  neutral  point,  corresponding  to  a  star  connected  voltage  of 
260  X  1.73  =  450  volts.  In  case  the  primary  coils  of  the 
furnace  are  connected  with  the  points  b1}  b2,  and  b  3,  we  give 
them  450  volts  in  place  of  the  500  volts  of  the  circuit.  Any 
number  of  these  taps  may  be  brought  out  of  the  auto-transformer. 
For  instance,  the  points  cl}  c2,  and  c3,  could  deliver  400  volts, 
provided  it  is  assumed  they  correspond  to  about  230  turns  so  that 
a  phase  voltage  of  230  would  result.  In  the  same  way  that  a 
voltage  decrease  is  attained  a  voltage  increase  may  also  be 
reached.  In  this  way  the  points  dly  d2)  and  d3  would  give 
550  volts,  and  the  points  e1}  e2,  and  e3,  a  potential  of  600, 
if  the  number  of  turns  per  core  were  raised  respectively  to  318 
and  347.  It  may  therefore  be  seen  to  be  a  matter  of  fact,  that 
the  voltages  are  proportional  to  the  number  of  turns,  and  that 
only  one  continuous  winding  per  core  of  the  transformer  can  be 
used  for  voltage  regulation.  A  so-called  step  switch,  especially 
designed,  is  still  necessary,  in  addition  to  this  transformer,  by 
the  aid  of  which  the  winding  may  be  switched  from  one  point 
to  another  without  interrupting  the  current. 

The  electrical  efficiency  of  a  Rochling-Rodenhauser  furnace 


THE  ROCHLING-RODENHAUSER    FURNACE  231 

may  be  regarded  as  extraordinarily  favorable,  for  an  electric 
furnace.  Measurements  taken  on  a  3^-ton  single  phase  furnace 
in  Volkingen,  for  instance,  gave  an  efficiency  of  96%,  notwith- 
standing that  this  furnace  was  the  first  of  the  larger  ones  to  be 
constructed,  and  could  by  no  means  be  designated  to  be  especially 
well  dimensioned — as  the  line  losses  are  extremely  low  when 
using  high  potential  directly,  and  as  rotary  transformer  losses 
are  usually  not  present,  the  total  electrical  efficiency  of  these 
furnaces  will  always  be  greater  than  90%. 

It  has  already  been  mentioned  that  the  furnaces  are  of  the 
tilting  variety. 

The  requirements  of  an  easily  surveyed  and  accessible  hearth 
may  be  regarded  as  being  fulfilled,  as  the  hearth  is  central  and 
has  two  or  three  operating  doors  at  the  sides.  There  remain,  of 
course,  the  heating  channels  at  the  sides  which  are  not  well 
esteemed  by  the  metallurgist,  although  they  are  so  arranged 
that  slag  cannot  enter  them,  but  it  must  be  remembered  that 
they  result  in  a  far-reaching  circulation  on  account  of  electrical 
conditions,  which  assures  a  homogeneous  composition  of  the 
molten  metal  both  in  the  channels  and  in  the  hearth,  so  that  the 
heating  channels,  as  a  matter  of  fact,  exercise  no  deleterious 
influence  on  the  operations. 

The  circulation  phenomena  in  Rochling-Rodenhauser  furnaces 
result  advantageously  owing  to  electric  and  magnetic  conditions. 
Referring  to  Fig.  99,  which  shows  a  hearth  of  a  single  phase  or  two 
phase  furnace,  the  arrows  show  the  direction  of  the  circulation, 
which  direction  may  easily  be  observed  in  actual  practise  by 
throwing  some  lime  dust  on  the  uncovered  metal  bath.  We  have 
also  the  circulation  of  the  bath  against  the  lining,  between  the 
bath  and  the  coil.  In  addition  to  this  it  may  be  observed  that 
the  molten  metal  is  somewhat  elevated  at  the  doors,  which  re- 
sults in  a  flow  of  the  fluid  mass  toward  the  middle  of  the  hearth 
on  the  one  hand,  and  toward  the  channels  on  the  other.  Both 
manifestations  may  be  defined  as  being  the  mildest  forms  of  the 
pinch  effect.  This  appears  as  shown  in  Chapter  III,  because 
the  fluid  conductor  flows  toward  the  point  of  higher  temperature. 
The  high  current  densities  are  to  be  found,  first,  in  the  middle  of 


232  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  hearth,  and  second,  in  the  heating  channels,  whereas  the  cur- 
rent densities  are  decidedly  the  lowest  at  the  broad  sides  of  the 
hearth  near  the  doors.  There  is  consequently  a  suction  action, 
first  on  the  part  of  the  channels,  and  again  on  the  part  of  the 
centre  of  the  hearth.  This  circulation,  based  on  the  pinch  effect, 
has  the  advantage  that  it  works  vertically  against  the  inner  lining, 
and  therefore  lessens  this  motion,  so  that  throughout  the  whole 
furnace  there  can  be  observed  only  a  slow  flow,  without  being 
violent  in  any  way.  A  part  of  the  ascending  motion  of  the 


FIG.  99. 


FIG.  loo. 


fluid  metal  at  the  doors  is  to  be  accounted  for  by  stronger 
heating  of  the  bath,  occasioned  by  the  heat  generated  by 
the  current  through  the  current-carrying  lining,  which 
naturally  results  in  a  rise  in  temperature  of  the  higher  heated 
material. 

Exactly  the  same  reasons  cause  the  circulation  phenomena  in 
the  three  phase  furnaces,  so  that  there  remains  little  to  be  said 
about  it.  Fig.  100  shows  the  circulation  phenomena  which  may 
be  observed  in  one  of  these  furnaces.  This  is  somewhat  different 
from  the  single  phase  furnace,  as  there  is  an  additional  circular 
motion  of  the  bath  between  the  three  cores.  This  rotary  motion 
is  the  result  of  a  rotating  field,  which  arises  between  the  three 
transformer  cores  and  has  a  similar  action  to  the  connected 


THE   ROCHLING-RODENHAUSER   FURNACE 


233 


stator  of  the  polyphase  motor,  by  means  of  which  the  armature 
is  caused  to  revolve.  This  comparison  must  not  lead  one  to  the 
erroneous  conclusion,  that  the  bath  rotates  at  the  same  speed 
as  the  rotor  of  a  motor  would  under  similar  conditions.  The 
motion  is  also  very  mild  here,  and  can  often  only  be  observed  by 


FIG.  101. — -Transformer  of  a  single  phase  furnace. 


throwing  fine  lime  on  the  bare  metal.  A  circulation,  such  as 
this,  possesses  distinct  advantages  for  the  metallurgical  process. 
It  causes  new  masses  of  metal  to  be  brought  into  contact  with 
the  refining  slag,  also  a  thorough  homogeneity  of  the  contents 
of  the  furnace,  and  finally  facilitates  the  separation  of  suspended 
particles  of  slag,  without  having  any  consequential  disadvantages. 
If,  now,  the  opinion  is  expressed  that  the  lining  does  not  stand 
up  well  under  the  action  of  the  circulation,  this  may  be  accounted 
for  by  the  fact  that  the  durability  of  the  lining  of  induction 


234     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

furnaces  was  short,  as  compared  with  that  of  arc  furnaces;  but 
the  lining  costs  per  ton  of  steel  were  not  higher  than  those  of 
arc  furnaces.  As  a  matter  of  fact  the  influence  of  the  circu- 
lation of  the  molten  metal  on  the  lining  is  almost  insignificant, 
for  the  wear  takes  place  only  at  the  slag  line  and  is  therefore 
only  to  be  accounted  for  by  the  chemical  action  of  the  slag, 
which  can  be  easily  proved  by  the  worn  lining  at  the  slag  line. 
Finally,  it  may  be  mentioned  that  the  Rochling  Iron  &  Steel 
Works  have  been  successful  in  constructing  the  refractory 
lining  of  Rochling-Rodenhauser  furnaces  to  withstand  the 
action  of  the  slag,  to  such  an  extent  that  the  durability  of  the 
hearth  compares  very  favorably  with  that  of  the  Girod  or  Stassano 
furnaces.  Even  so,  the  bottoms  and  side  walls  of  20-ton  fur- 
naces, in  order  to  last  more  than  a  few  heats,  have  to  be  made 
of  Austrian  magnesite,  carefully  prepared,  and  the  different 
sized  grains  selected  and  proportioned  in  accordance  with  an 
empirical  formula,  the  entire  mass  mixed  with  a  special  grade 
of  tar.  When  these  conditions  are  not  obtainable  the  furnace 
becomes  inoperative. 

Regarding  the  circulating  phenomena,  there  is  still  to  be 
mentioned  that  with  very  large  furnaces,  for  instance,  having 
comparatively  great  depths  of  bath,  it  may  be  advisable  to 
obtain  a  stronger  motion  in  the  bath  than  is  possible  with  the 
above-mentioned  forces.  A  convenient  means  for  doing  this  is 
to  increase  the  pinch  effect.  In  order  that  this  may  be  ac- 
complished, all  that  is  required  is  to  raise  the  bottom  of  the 
hearth  in  the  centre  for  a  short  length.  This  causes  a  con- 
traction of  the  cross-section  of  the  bath  at  this  place,  giving  a 
higher  density,  and  consequently  a  stronger  suction  action  at 
the  centre  of  the  bath  which  can  be  increased  until  the  bath 
becomes  wavy,  in  case  the  raised  portion  is  made  high  enough. 
By  means  of  this  arrangement,  therefore,  we  have  a  convenient 
means  of  increasing  the  circulating  motion  to  any  desired 
degree. 

The  Rochling-Rodenhauser  furnace  is  far-reaching  in  its 
application.  The  furnaces  are  adapted  to  produce  any  quality 
of  steel  from  any  common  raw  material.  The  assurance  for  this 


THE   ROCHLING-RODENHAUSER   FURNACE  23.r) 


FIG.  102.— Transformer  of  a  three  phase  furnace. 


23G  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

is  given  by  the  similarity  of  the  working  hearth  to  that  of  the 
Siemens-Martin  open-hearth  furnace.  It  does  not  seem  inap- 
propriate to  dwell  explicitly  on  this  point  at  this  place,  as  these 
furnaces,  being  a  type  of  induction  furnace,  were  credited  with 
the  same  weaknesses  that  the  early  induction  furnaces  possessed. 
These  disadvantages  appeared  with  the  Kjellin  furnace  (the 
first  induction  furnace  which  found  its  way  into  practical  steel 
making)  on  account  of  its  peculiarly  shaped  hearth.  This 
prejudice  against  the  furnaces  is,  however,  entirely  unjust.  Re- 
garding this,  reference  is  made  to  the  second  part  of  this  book, 
where  the  best  refining  results  attained  with  other  electric 
furnaces,  as  well  as  with  Rochling-Rodenhauser  furnaces,  are 
discussed  in  detail.  Of  course  these  furnaces  reach  a  limit  of 
their  applicability,  when  cold  stock  is  to  be  melted  in  the  same 
furnace  for  high  class  steel  alloys  with  quick  changes  following 
each  other.  In  this  case,  when  working  up  cold  stock,  the  metal 
remaining  in  the  hearth  would  interfere  with  the  composition  of 
the  next  charge.  Therefore,  if  induction  furnaces  were  to  be 
used  in  this  case,  two  furnaces  would  be  necessary,  one  of  which 
would  be  designated  to  melt  the  cold  metal,  and  be  operated  to 
make  a  portion  of  each  charge  start  the  succeeding  charge, 
while  the  second  furnace,  in  which  the  refining  and  alloys  would 
be  made,  could  always  be  charged  with  hot  metal  from  the  first 
furnace,  and  would  consequently  be  fully  emptied  after  each 
charge.  With  this  method  of  operation  it  is  evident  that  the 
previous  charge  cannot  in  any  way  affect  the  quality  of  the 
succeeding  one.  It  requires,  however,  a  comparatively  large 
initial  capital,  which  would  only  be  justified  when  it  would  be 
desired  to  make  large  quantities  of  electric  steel.  These  con- 
ditions would  make  it  difficult,  if  not  impossible,  for  small  steel 
plants  to  compete  with  the  induction  furnace  in  its  present 
form,  when  using  the  above  method.  On  the  other  hand,  in 
very  many  other  cases,  the  necessity  of  leaving  some  of  the 
metal  in  the  furnace  can  hardly  be  regarded  as  a  detriment  when 
working  up  scrap.  This  applies  particularly  to  those  making 
electric  steel,  in  the  manner  it  is  made  to-day,  for  instance,  in 
large  lots  to  take  the  place  of  Swedish  iron.  For,  in  this  case, 


THE   ROCHLING-RODENHAUSER   FURNACE  237 

the  metal  remaining  offers  the  advantage  of  allowing  the  melting 
operation  to  proceed  by  using  a  considerable  proportion  of  the 
available  electric  energy  left  in  the  remaining  metal,  even  while 
charging.  This  results  in  shortening  the  melting  time,  and 
produces  a  better  efficiency  and  also  a  greater  production. 

A  further  limitation  of  the  use  of  electric  furnaces  may  be 
ascertained  by  studying  the  limit  of  practicability  of  the  furnaces 
according  to  their  size.  It  may  be  mentioned  here,  that  single 
phase  and  two  phase  furnaces  are  built  for  a  minimum  capacity 
of  300  kg.  (660  lb.),  and  give  practical  and  economically  useful 
operating  conditions.'  If  the  bath  surface  becomes  too  large 
in  proportion  to  the  capacity,  then  the  thermal  losses  become  of 
such  an  extent  that  an  economical  operation  would  no  longer 
be  possible.  The  useful  limits  of  these  furnaces  for  the  iron 
industry  lie  therefore  within  the  sizes  mentioned  above  and 
below. 

One  of  the  largest  European  Rochling-Rodenhauser  furnace 
units  so  far  built  has  a  capacity  of  8  to  10  tons.  This  gives  ex- 
cellent operating  results  at  the  works  of  the  Rochling  Iron  & 
Steel  Works.-  Since  then  a  i3~ton  furnace  has  been  placed  in 
operation  at  the  Poldhi  Works  in  Austria,  and  is  reported  to  be 
working  well.  Two  2o-ton  furnaces  are  ready  to  be  placed  in 
operation  in  Pennsylvania.  (See  Fig.  101.) 

The  thermal  efficiency  of  the  furnace  may  best  be  judged  by 
the  total  efficiency.  That  the  efficiency  of  furnaces  becomes 
better  with  increasing  sizes,  is  true  as  it  is  with  other  furnaces 
previously  discussed.  We  find  that  the  smaller  sizes,  adapted 
to  single  phase,  are  considerably  superior  to  the  three  phase, 
considering  their  total  efficiency,  whereas  when  the  capacity 
reaches  3  tons  the  efficiencies  are  about  equal,  while  for  larger 
sizes  than  this  the  polyphase  furnace  is  the  better.  The  reason 
for  this  arises  from  the  fact  that  single  phase  furnaces,  even  of 
the  3-ton  size,  must  be  operated  from  as  low  as  25-cycles,  whereas 
three  phase  furnaces  of  this  size  may  be  operated  to  advantage 
with  50  cycles.  Lowering  the  frequency  necessitates  enlarging 
the  cross-section  of  the  transformer,  which  means  more  space 
for  the  coils,  and  hence  a  larger  periphery  of  the  walls  touching 


238   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  bath  surface,  so  that  with  a  3-ton  single  phase  furnace  we 
have  a  larger  bath  surface,  with  a  lesser  bath  depth,  than  with  a 


FIG.  103. 

three  phase  furnace  of  the  same  size,  which  has  a  smaller  bath 
surface  with  a  greater  depth  of  bath. 

Even  though  the  single  phase  furnace  up  to  the  3 -ton  size  is 
preferable  to  the  three  phase  furnace  on  account  of  its  efficiency, 
these  conditions,  however,  become  a  deciding  factor  only  when  a 
new  generator  is  to  be  furnished  for  the  furnace  in  either  case.  If, 
on  the  other  hand,  an  extensive  power  plant  producing  a  certain 
type  of  current  already  exists,  then  the  choice  of  furnaces 
would  in  most  cases  be  decided  by  the  actual  current  available, 
in  case  this  could  be  used  directly  in  a  single,  two,  or  three 
phase  furnace.  In  these  cases,  when  using  the  existing  current 
directly  in  the  furnace,  the  deciding  factor  would  be  the  avoidance 
of  the  rotary  transformer  losses,  which  are  always  about  15  to 
20%,  and  therefore  so  large  that,  as  fai  as  the  total  efficiency  of 
a  furnace  installation  is  concerned,  they  would  be  bound  to  be 
the  deciding  factor. 


THE   ROCHLING-RODENHAUSER   FURNACE  239 

In  discussing  the  question  of  efficiency,  the  following  will  be 
of  interest:  The  total  (net)  efficiency  of  a  i^-ton  three  phase 
furnace  at  the  Rochling  Iron  &  Steel  Works  was  60%,  when 
comparing  the  theoretical  figures  and  the  actual  amount  of 
energy  used  in  melting  up  cold  scrap.  The  total  efficiency  of 
the  8-ton  furnace  operating  at  Volklingen  was  determined  by  the 
fact  that  it  took  580  kw.  hrs.  to  melt  one  ton  of  common  scrap. 
If  we  compare  this  with  the  required  theoretical  energy,  which 
was  placed  at  489  kw.  hrs.  in  the  previous  chapter,  we  find  that 
the  8-ton  Rochling-Rodenhauser  single  phase  furnace  has  an 

efficiency  of  — -  =  85%.    Since  this  calculation  of  489  Kw.-hrs. 
580 

was  made,  Jos.  W.  Richards  has  placed  this  figure  at  348  Kw.-hrs., 

making  the  above  —  =  60%. 
580 

Even  though  these  figures  may  not  be  called  absolutely 
correct,  on  account  of  unavoidable  irregularities  or  uncertainties 
creeping  into  the  theoretical  computations  of  the  energy  required, 
still  the  fact  remains  that  the  required  power  of  580  kw.  hrs.  was 
all  that  was  needed  to  melt  one  ton  of  common  commercial  steel 
scrap,  so  that  the  efficiency  figures  retain  their  full  accuracy  and 
significance  as  relative  figures  of  comparison.  Considering  the 
heat  losses,  these  results  show  that,  in  spite  of  the  really  unfavor- 
able arrangement  of  the  hearth  with  the  side  connecting  channels, 
efficiencies  are  still  attained,  which  are  fully  equal  to  those 
of  the  Kjellin  furnace,  with  its  ring  formed  hearth,  and  they  may 
also  be  considered  as  comparing  most  favorably  with  the 
efficiency  of  any  arc  furnace. 

In  adding  a  few  words  here  on  the  installation  cost,  reference 
is  made  to  a  5-ton  polyphase  furnace  which  is  to  be  connected  to 
an  existing  power  plant.  This  would  operate  in  conjunction 
with  a  separate  transformer  and  a  multi-point  switch  and  would 
cost  about  $28,000.  This  price  includes  the  furnace,  the  furnace 
transformer,  the  switchboard,  the  electrical  tilting  mechanism, 
etc.  It,  however,  does  not  include  the  generator  installation, 
which  was  assumed  to  be  already  in  existence. 

The  following  references  are  to  the  figures  which  augment 
the  text.  Fig.  101  shows  the  transformer  of  a  single  phase 


240   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Rochling-Rodenhauser  furnace,  while  Fig.  102  shows  the  trans- 
former for  a  three  phase  furnace.  From  the  figures  one  can 
plainly  perceive  the  arrangement  of  the  cores  and  yokes.  The 
former  are  covered  by  the  protecting  cylinders,  as  these  figures 
show  the  manner  in  which  the  ventilating  air. is  conveyed  by 
means  of  a  central  air  duct,  as  shown  in  Fig.  88.  The  bifurcated 
air-supply  duct  which  lies  between  this  central  duct  and  the  cores 


FIG.  104. 


is  also  plainly  distinguishable  in  Fig.  102.  Such  furnace  trans- 
formers are  then  built  directly  into  the  furnace  brickwork  or  into 
the  furnace  refractories,  which  thus  decide  the  appearance  of 
the  furnace.  Fig.  103  shows  an  8-ton  single  phase  furnace  in 
its  tilted  position,  and  Fig.  104  a  three  phase  furnace  of  1^2  tons 
capacity. 

The  sale  of  these  furnaces  and  the  giving  of  licenses  are  con- 
ducted in  Continental  Europe  by  the  Gesellschaft  fur  Elektro- 
stahlanlagen,  Berlin,  Nonnendamm;  for  England  and  her  Colonies 
except  Canada  by  the  Grondal-Kjellin  Co.,  London.  In  the 
United  States  and  Canada  formerly  by  the  American  Electric 
Furnace  Co.,  New  York,  at  present  by  Naylor  6*  Co.,  agents 
for  Grondal-Kjellin  Co.,  New  York. 


CHAPTER  XIV 
THE  ELECTRIC   SHAFT  FURNACE 

IN  the  consideration  of  electric  furnaces  that  one  must  not 
be  overlooked  which  may  be  briefly  called  the  Electric  Shaft 
Furnace.  It  is  to  serve  to  replace  the  ordinary  blast  furnace. 

From  early  times  efforts  have  been  made  in  countries  rich 
in  ore  and  water-power,  but  poor  in  fuel,  to  replace  the  fuel  used 
in  the  blast  furnace  for  the  production  of  heat,  by  electricity, 
and  so  lower  the  fuel  consumption.  In  the  electrical  process  of 
pig-iron  production  there  only  remains  about  one-third  of  the 
fuel  consumption  necessary  in  the  ordinary  blast  furnace,  and 
this  is  for  reduction  only.  In  this  way  about  two-thirds  of  the 
fuel  cost  is  saved.  At  the  same  time  the  large  blowing  engines 
of  the  ordinary  blast  furnace  are  not  required.  These  are  the 
two  important  things  that  promise  success  to  a  good  solution 
of  the  question  of  the  electrical  smelting  of  iron  ore. 

Even  in  the  introductory  period  of  practically  useful  electric 
furnaces  we  find  that  they  were  first  adapted  to  the  production 
of  pig  iron.  The  Stassano  furnace  is  an  example  which  was 
originally  only  constructed  for  the  smelting  of  ore.  It  is  shown 
in  Fig.  44,  which  clearly  brings  out  how  similar  it  is  in  construc- 
tion to  the  ordinary  blast  furnace.  Stassano's  experiment  was 
unsuccessful,  and  we  have  seen  how  he  turned  to  the  method 
worked  out  in  the  meantime  at  La  Praz  by  Heroult,  for  the 
utilization  of  scrap.  Tests  were  also  made  in  those  parts  of 
France  having  abundant  water-power.  Here  Keller  and  Heroult 
were  occupied  with  the  question,  and  many  reports  and  discus- 
sions of  their  experiments  appeared  in  the  journals  in  the  middle 
of  the  last  decade. 

The  furnace  used  by  Keller  is  shown  in  outline  in  Fig.  105. 
Two  shafts  are  joined  at  the  bottom  by  means  of  a  channel. 
At  the  base  of  each  shaft  is  a  carbon  electrode,  these  electrodes 

24  It 


242    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


being  connected  by  means  of  an  outside  cable.  A  carbon  elec- 
trode is  hung  in  each  shaft.  At  the  beginning  of  the  operation 
the  current  flows  from  one  carbon  electrode  and  through  the 
charge  in  the  corresponding  shaft  to  the  bottom  electrode. 
From  here  it  goes  through  the  outside  cable  to  the  bottom 
electrode  of  the  other  shaft,  through  the  charge,  and  to  the 
second  electrode.  As  the  smelting  proceeds  the  connecting 

channel  becomes  filled  with 
molten  iron.  As  soon  as  a 
connection  is  made  in  this 
way  between  the  two  shafts 
the  current  flows  through  the 
molten  material,  which  offers 
a  much  lower  resistance  than 
the  two  bottom  electrodes 
and  the  outside  cable.  In  the 
middle  of  the  channel  is  the 
tapping  hole. 

In  a  later  construction 
Keller  had  a  third  small 
carbon  electrode,  which  was 
lowered  into  the  connecting 

channel,  and  was  used  to  keep  the  metal  there  thoroughly  liquid. 
Extensive  tests  were  made  with  this  later  furnace  at  Livet  in 
1904.  at  the  time  of  the  visit  of  the  Canadian  Commission  under 
Dr.  Haanel. 

Of  lesser  importance  were  the  tests  carried  out  by  Heroult, 
at  La  Praz,  in  the  presence  of  the  Commission.  German  Patent 
142,830,  1902,  shows  that  Heroult  had  not  left  the  subject  of 
the  smelting  of  ore  in  the  electric  furnace  without  attention, 
although  he  worked,  at  first,  to  develop  a  process  for  using  scrap- 
iron  and  steel.  This  patent  was  granted  on  an  electric  furnace 
with  electrodes  built  in  the  hearth  and  the  shaft.  It  is  shown 
in  Figs.  106  and  107.  It  was  not  successful,  and  Heroult  in  his 
tests  before  the  Commission  mostly  used  a  simple  type  similar  to 
one-half  of  the  Keller  furnace.  His  average  production  with  such 
a  furnace  at  that  time  was  7.82  metric  tons  per  1000  E.H.P.  days. 


FIG.  105. 


THE  ELECTRIC  SHAFT  FURNACE 


243 


In  the  time  immediately  following  the  visit  of  the  Canadian 
Commission  no  further  experiments  in  the  line  of  pig-iron  pro- 
duction were  made  in  Europe  that  are  worthy  of  notice.  The 
general  attention  was  devoted  to  the  production  of  electric  steel 
and  iron  for  the  very  good  reason  that  the  results  so  far  obtained 


FIG.  1 06. 


FIG.  107. 


in  the  production  of  pig  iron  showed  no  promise  of  success  in 
Europe,  for  a  great  number  of  years,  in  competition  with  the 
highly  developed  ordinary  blast-furnace  process. 

On  the  other  hand  tests  were  continued  in  Canada,  to  which 
country  Heroult  went  in  December,  1905,  his  experiments  being 
made  in  January,  1906.  They  were  mostly  carried  out  with  the 
furnace  shown  in  Fig.  108,  consisting  of  a  crucible  with  a  shaft 
above  it.  The  bottom,  being  made  of  electrode  carbon,  forms 
one  pole,  the  other  being  a  hanging  carbon  electrode.  This 
electrode  had  a  length  of  about  5'  10.8",  and  a  cross-section  of 
about  16"  x  16".  The  maximum  current  was  about  5000 
amperes,  with  a  pressure  of  35  to  40  volts  and  a  power  factor  of 
cos  </>  =  0.9.  The  results  under  normal  conditions  were  the 
production  of  about  11.5  metric  tons  of  pig  iron  per  1000  E.H.P. 
days.  Although  good  results  were  obtained  with  various  ores, 
judging  from  a  metallurgical  standpoint,  it  was  seen  that  an 
electrode  entering  the  furnace  with  the  charge  would  not  satis- 
factorily solve  the  problem.  For  instance  the  electrode  frequent- 


244   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


ly  rose  higher  and  higher  in  the  shaft  of  the  furnace,  so  that  the 
material  in  the  bottom  got  colder  and  colder.  This  was  caused 
by  the  charge  becoming  too  dense,  and  not  allowing  the  gases 

to  escape  easily  enough. 
In  this  way  the  resist- 
ance between  the  two 
poles  was  lessened,  and 
the  voltage  remaining  the 
same,  the  upper  electrode 
rose  in  the  furnace.  It 
also  brought  about  con- 
siderably higher  electrode 
consumption.  To  sum 
up  the  question,  a  suc- 
cessful electric  shaft  fur- 
nace was  not  solved  by 
the  experiments  made  in 
Canada. 

In  the  spring  of  1907, 
experiments  with  electric 
pig-iron  production  were 
begun  in  Sweden.  Messrrs. 
Gronwall,  Lindblad  and 
Stalhane  together  formed 
the  "Electrometal" 
Company,  with  the  aim 
of  building  and  selling 
electric  furnaces.  The 
tests  which  will  now  be 
considered  in  detail  were 
carried  out  by  them  at 
FIG.  108.  Domnarfvet.  According 

to  Yngstrom's  careful  re- 
port in  the  Jern-Kontorets  Annaler,  No.  9,  1909,  a  current  of 
7000  volts  at  60  periods  was  used.  With  this  current  a  900 
HP  motor  was  driven,  directly  coupled  to  a  25  period,  three  phase 
generator.  From  this  generator  the  current  was  led  directly 


TITE  ELECTRIC  SHAFT  FURNACE 


245 


to  the  transformers  which  were  arranged  near  the  furnaces  and 
served  them.  Here  also  a  switphboard  with  the  necessary 
measuring  instruments  was  set  up.  These  included  a  watt- 
meter, three  ammeters,  and  one  voltmeter.  Underneath  were 
the  hand  wheels  for  regulating  the  electrodes. 

Gronwall,  Lindblad  and  Stalhane  first  made  use  of  the  results 
of  the  former  experiments.  They  therefore  endeavored  to 
completely  obviate  the  use 
of  hanging  electrodes,  and 
to  keep  the  current  in  the 
hearth  of  the  furnace.  Fig. 
109  shows  the  first  test 
furnace,  which  was  built 
to  take  single  phase  cur- 
rent. Each  pole  consists 
of  a  copper  plate  carrying 
a  graphite  block.  These 
blocks  are  hollowed  and  lie 
outside  of  the  furnace 
proper.  Channels  lead  from 
them  into  the  furnace 
which,  when  filled  with 
molten  iron,  serve  to  con- 
duct the  current  to  and 
through  the  charge.  Be- 
sides these  two  conduction  FIG.  109. 
channels  that  are  arranged 

on  one  side  of  the  furnace,  there  is  a  third  one,  as  may  be  seen 
in  the  illustration,  and  which  serves  for  tapping  the  furnace. 

After  charging,  the  furnace  is  run  precisely  as  an  ordinary 
blast  furnace,  until  a  considerable  amount  of  metal  has  collected 
in  the  hearth.  This  insures  good  conduction  from  the  carbon 
electrodes  to  the  interior.  The  blast  is  then  stopped,  the  current 
switched  on,  and  the  electric  heating  begun. 

The  course  of  the  current  was  arranged  as  follows:  It 
entered  at  one  pole  and  passed  through  the  metal  lying  over  it 
into  the  metal  in  the  channel  at  one  side  of  the  furnace  proper, 


246  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

from  here  through  the  charge  to  the  metal  in  the  channel  at 
the  other  side,  and  so  to  the  outgoing  pole.  Heating  is  brought 
about  through  an  overheating  of  the  liquid  contents  of  the 
furnace  on  the  one  hand,  and  the  resistance  offered  by  the  charge 
on  the  other.  This  should  furnish  heat  sufficient  to  smelt  the 
ore.  The  hearth  was  made  of  quartz.  In  operation  it  only 
lasted  a  very  short  time,  so  that  the  furnace  could  not  be  operated 
for  very  long.  This  was  because  its  wave-like  surface  offered 
conditions  favorable  to  attack,  and  brought  about  quick  destruc- 
tion at  the  high  temperatures  reached. 

The  first  necessity  was  to  rebuild  the  furnace.     This  was 
done  in  such  a  way  that  the  electrodes  led  into  the  furnace  from 
opposite  sides,  as  is  shown  in  Fig.  1 10.     At  the 
,  same  time  it  was  hoped  that  the  use  of  mag- 

nesite  in  the  hearth  would  give  better  service. 
This,  however,  was  not  the  case,  for  the  reason 
that  the  magnesite,  a  fairly  good  conductor 
even  at  ordinary  temperatures,  became  too  good 
a  conductor  at  a  high  temperature,  and  the  ex- 
periment had  to  be  stopped.  This  second  test 
'  showed  the  impossibility  of  satisfactorily  lead- 

FIG.  no.          ing  the  strong  current  necessary  for  heating  a 
shaft  furnace  into  the  charge  from  the  bottom. 
This  style  of  furnace  was  therefore  rejected. 

The  third  test  furnace  approximates  in  form  the  one  already 
proposed  by  Heroult  in  his  patent  of  1902.  It  is  shown  in 
Fig.  in.  The  shaft-like  construction  is  furnished  with  three 
electrodes,  of  which  one  forms  the  bottom,  while  the  two  others 
are  arranged  on  opposite  sides  at  a  medium  height.  The  direction 
of  the  current  can  be  so  arranged  that  it  either  flows  horizontally 
from  one  shaft  electrode  to  the  other,  or  else  goes  out  through 
the  bottom  electrode.  In  operation  the  shaft  electrodes  were 
destroyed  so  rapidly  that  they  were  replaced  by  ordinary  water 
cooled  electrodes  with  continuous  feed.  With  this  arrangement 
considerably  better  results  were  obtained,  but  the  walls  near 
the  shaft  electrodes  were  so  rapidly  destroyed,  because  of  the 
intense  heat  generated,  that  this  style  of  furnace  was  also  rejected 


THE  ELECTRIC  SHAFT  FURNACE 


247 


as  unsatisfactory.  It,  however,  pointed  the  way  to  a  good 
solution  of  the  question.  If  care  was  taken  to  keep  the  intense 
heat,  which  is  produced  where  the  electrodes  and  charge  come 
in  contact,  away  from  the  walls,  then  more  favorable  results 
and  a  greater  furnace  life  would  be  obtained.  These  considera- 
tions led  to  surrounding  the  electrodes  directly  with  the  charge, 
so  that  the  heat,  which  was  formerly  lost  through  the  walls,  could 
now  be  used  for  heating  the  charge, 
and  at  the  same  time  a  much 
greater  durability  of  the  furnace 
walls  was  obtained. 

The  1909  test  furnace  is  shown 
in  Fig.  112,  the  lower  part  of 
which  may  be  considered  as  the 
final  form  of  the  electric  shaft 
furnace.  This  is  the  furnace  of 
Gronwall,  Lindblad  and  Stalhane. 
It  has  three  electrodes  penetrat- 
ing the  roof  of  this  hearth  and 
is  in  general  very  similar  to  the 
ordinary  blast  furnace,  except  that  the  tuyeres  are  replaced  by 
electrodes.  The  results  show  that  this  construction  in  its  1911 
and  1912  improved  form  is  the  most  complete  and  suitable 
produced,  and  is  perhaps  the  only  one  worthy  of  serious  considera- 
tion. A  detailed  description  is  given  below. 

The  smelting  part  of  the  1909  furnace  forms  a  large  crucible 
or  hearth  f  4%"  in  diameter,  4'  n"  high.  It  is  lined  with  mag- 
nesite.  The  shaft  of  the  furnace  is  arranged  above  the  hearth, 
and  has  a  height  of  if  with  an  interior  diameter  of  4'  3"  at  the 
widest  part.  The  shaft  is  supported  by  a  steel  framework 
resting  on  six  iron  columns.  This  makes  it  possible  to  independ- 
ently repair  the  hearth.  The  charge  falls  from  the  shaft  into 
the  hearth  through  an  opening  arranged  in  the  roof.  It  forms 
an  angle  or  slope  of  about  50°  to  55°.  This  produces  a  free  space 
between  the  charge  and  the  roof  and  walls  of  the  hearth,  on 
which  the  greatest  importance  is  to  be  placed.  It  serves  to 
cool  the  electrodes  and  the  walls  of  the  furnace.  To  help  in  this 


FIG.  in 


248   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

purpose  the  cool  waste  gases  from  the  top  of  the  shaft  are  taken 
and  blown  through  tuyeres  into  this  cooling  space.  This  method 
also  brings  heat  back  to  the  furnace,  and  so  gives  a  better  heat 
efficiency.  As  Fig.  112  shows,  three  carbon  electrodes  penetrate 
the  roof  of  the  hearth.  In  the  1910  model  four  electrodes,  and  in 
the  1911-1912  model  six  electrodes,  are  used.  The  early  electrode 

_B 


FIG.  112. 

consisted  of  two  carbon  blocks  13"  square,  so  that  the  total  cross- 
section  is  169  sq.  ins.  The  electrodes  are  made  in  Sweden  from 
retort  carbon,  and  permit  the  use  of  a  current  of  25.8  amperes 
per  sq.  in. 

The  electrode  holders  consist  of  strong  steel  frames.    These 


THE  ELECTRIC  SHAFT  FURNACE  249 

are  provided  with  several  wedges  by  means  of  which  the  copper 
plates  that  carry  the  current  from  the  cables  to  the  electrodes 
are  firmly  pressed  against  the  latter.  The  electrodes  are  operated 
by  hand,  and  the  part  projecting  from  the  furnace  is  provided 
with  an  asbestos  cover  to  prevent  oxidation.  The  openings  for 
the  electrodes  have  water-cooled  seats,  and  arrangements  are 
provided  to  prevent  the  escape  of  gas,  which  is  most  important. 

When  the  furnace  is  put  in  operation  it  is  run,  at  first,  exactly 
like  an  ordinary  blast  furnace.  The  electrical  heating  is  only 
used  later.  The  furnace  now  described  was  run,  with  slight 
interruptions,  from  May  7, 1909,  to  the  end  of  July.  The  follow- 
ing notes,  taken  from  the  account  of  the  operations,  are  of  special 
interest.  At  the  beginning  of  the  electric  heating  the  current 
goes  chiefly  through  the  upper  part  of  the  charge,  which  means 
that  the  largest  amount  of  heat  is  produced  immediately  under 
the  roof,  which  is  strongly  heated  and  partly  destroyed.  One 
reason  for  this  is  that  the  lower  part  of  the  charge  is  colder,  and 
therefore  offers  greater  resistance  than  the  upper  part.  The 
conditions  were  greatly  improved  as  soon  as  the  waste  gases 
were  blown  in.  The  temperature  of  the  roof  was  lowered,  and 
the  hottest  zone  sank  lower  and  lower.  The  result  was  a  lower- 
ing in  the  resistance  of  this  part  of  the  charge,  so  that  the  current 
found  a  more  favorable  path,  and  was  concentrated  in  the  lower 
part  of  the  hearth.  When  this  condition  was  once  reached  a 
five  days'  interruption  of  the  gas-cooling  brought  about  no  change 
from  normal  running. 

During  the  operation  of  the  furnace  no  big  fluctuations  of 
the  current  were  noticed,  and  even  during  tapping  the  instru- 
ments remained  steady.  This  leads  to  the  conclusion  that  the 
resistance  of  the  charge  was  very  constant.  The  electrodes 
required  very  little  attention.  They  were  regulated  once  a  day 
on  the  average,  and  in  one  case  they  were  not  touched  for  five 
days. 

The  maximum  current  amounted  to  9000  amperes  per  phase. 
With  25  cycles  a  power  factor  of  0.8  to  0.9  was  obtained,  with 
60  cycles  of  about  0.7,  and  other  calculations  gave  0.535.  Natu- 
rally with  a  fixed  cross-section  of  electrodes  the  amount  of  energy 


250  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


that  can  be  used  is  dependent  upon  the  permitted  potential, 
which  in  its  turn  depends  upon  the  resistance  of  the  charge. 
The  higher  this  resistance,  the  higher  can  the  voltage  be  without 
the  strength  of  current  overstepping  the  permitted  maximum. 
It  is  therefore  of  interest  to  know  how  to  influence  the  internal 
resistance,  and  this  consists  in  the  choice  of  the  proper  amounts 
of  ore  and  fuel  in  the  charge.  In  the  following  table  are  given 
the  strengths  of  current  reached  with  various  burdens,  and  with 
fixed  voltages. 


Charge  with 

Potential 
between  two 
Two  Phases 
in  Volts 

Current 
Strength 
per  Phase 
Amperes 

Power 
with  an 
Average  Cos 
<t>  =  0.85 
A  =  1.73  ei  cos  <£ 

Coke  in  excess                           

34 

9,6OO 

480  kw. 

Coke  not  in  excess   

36 

8,800 

465     " 

Too  little  charcoal.  .  .  '.  
Sufficient  charcoal  
Too  much  charcoal 

60 

54 
48 

6,300 
7,600 
7,6OO 

555     " 
603     " 
536     " 

Too  much  coke  and  charcoal 

35 

9.2OO 

471     " 

Sufficient  coke  and  charcoal         .... 

48 

7,6OO 

536     " 

The  operation  of  the  furnace  was  very  simple  and  uniform, 
the  metal  being  tapped  about  every  six  hours.  When  judging 
the  efficiency  of  the  furnace  it  should  be  remembered  that  the 
following  sources  of  loss  are  to  be  considered: 

1.  Cooling  of  the  electrodes  with  water. 

2.  The  ohmic  resistance  of  the  conductors  and  contacts. 

3.  The  radiation  from  the  furnace. 

The  total  loss  amounted  to  from  230  to  270  kw.,  the  higher 
value  coming  at  the  end  of  the  run.  The  loss  is  divided  about 
as  follows:  The  water  cooling  carries  away  from  118  to  225 
kw.,  which,  with  a  power  of  about  500  kw.,  corresponds  to  a 
loss  of  about  25  to  30%.  Overcoming  the  contact  resistance 
takes  about  40  kw.,  and  from  no  to  180  kw.  are  lost  by 
radiation.  The  electrodes  lose  5.8  kg.  (12.8  Ib.)  per  metric 
ton  by  burning  away,  the  total  consumption  being  13.8  kg. 
(30.4  Ib.)  per  metric  ton.  From  another  source  (E.  F.  Ljung- 


THE  ELECTRIC   SHAFT  FURNACE 


251 


berg,  Metallurgie,  November,  1909),  the  consumption  of  elec- 
trodes through  burning  is  8.8  kg.  (19.4  lb.),  and  through  waste 
ends  13.9  kg.  (30.6  lb.),  a  total  of  22.7  kg.  (50  lb.)  per  metric 
ton.  This  large  difference  between  the  loss  by  burning  and  the 
total  consumption  is  brought  about  by  the  electrodes  not  being 
completely  burnt,  and  the  ends  having  to  be  replaced  by  new 
ones.  There  is  no  loss  from  stub  ends  in  the  later  designed 
electrodes  which  are  screwed  together. 

The  maintenance  cost  of  the  furnace  could  not  be  determined 
exactly,  but  the  furnace  worked  satisfactorily  for  85  days  without 
a  stop.  The  weakest  place  is  the  roof  of  the  hearth,  which  is 
exposed  to  the  intense  heat  generated  at  the  electrodes.  Accord- 
ing to  Ljungberg,  891,623  kw.  hours  were  used  to  produce  280  met- 
ric tons.  This  means  0.492  h.p.  years  or  3184  kw.  hours  per  metric 
ton  of  pig  iron.  This  is  a  high  figure  and  has  since  been  lowered 
to  less  than  2000  kw.  hours,  or  0.31  h.p.  years,  on  long  runs.* 

The  following  tables  give  the  efficiency  obtained  during  the 
test  with  different  burdens: 


Charge  No. 

Carbon  Consumption 
(pure  carbon) 

Amount  of 
Theoretical 
Energy  Neces- 
sary with  the 
Given  Carbon 

Real  Power 
Consumption 

Electrical 
Efficiency 

Kg. 

Lb. 

Consumption 
kw.  hrs. 

kw.  hrs 

H.P.Year 
365  days 

3 

252 

555-5 

1,470 

3,H4 

0.483 

47% 

4 

254 

560.0 

1,438 

2,473 

0.383 

58 

5 

284 

626.1 

1,741 

3,245 

0.505 

54 

6 

294 

648.1 

1,870 

3,334 

0.517 

56 

The  economy  of  making  pig  iron  in  the  Gronwall,  Lindblad 
6*  Stalhane  furnace  is  given  in  the  chapter  on  operating  costs, 
hence  the  following  table  by  Catani  is  of  interest.  It  is  quoted 
from  Neumann,  Stahl  und  Eisen,  1909,  p.  276.  This  table 
shows  how  high  the  price  of  cufrent  per  h.p.  year  can  go,  with 
coke  at  a  fixed  price,  for  the  electric  shaft  furnace  to  compete 
favorably  with  the  ordinary  blast  furnace: 

*  See  page  250. 


252  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Pig  Iron  Produced 
per  24  hrs.  per  H.  P. 

Coke  Price 

Kg. 

Lbs. 

$3.81 

IS-  7i 

$7.6l 

6 

13.2 

4.88 

7-30 

9-76 

1        Price  of 

3 

I7.6 

6.09 

9.14 

12.  19 

\         Power 

IO 

22.  O 

7.6l 

11.42 

15.23 

f           Per 

12 

26.4 

8-57 

12.85 

17.14 

J       h.p.  year 

For  comparison  with  the  foregoing  figures  of  the  first  tests 
in  1909,  the  1910-1911  tests  results  are  here  recorded. 

The  November,  i9io-April,  1911,  test  furnace  of  2500  h.p., 
of  Gronwall,  Lindblad  &  Stalhane,  is  shown  in  vertical  cross- 
section  by  Fig.  125.  During  the  run  the  furnace  was  operated 
with  four  electrodes  penetrating  the  roof,  the  furnace  being 
operated  with  two  phase  current,  from  a  three  phase  circuit  by 
means  of  Scott  connected  transformers.  The  incoming  current  is 
10,000  volts,  three  phase,  25  cycles.  The  secondary  volts  can 
be  regulated  between  50  and  90  volts  from  the  high  tension  side. 
The  arrangements  are  such  that  the  different  phases  can  work 
simultaneously  with  different  voltages.  The  method  has  greatly 
facilitated  the  working.  Regulation  is  also  had  by  different 
switching  from  the  low  tension  side.  The  newer  3500  h.p. 
furnaces  for  Hardanger,  Norway,  using  coke  instead  of  charcoal, 
have  the  following  dimensions: 

Diameter  of  hearth 3        meters  =  10  ft. 

at  ring 1.5         "      =   5  " 

"         at  boshes 2.15       "      =   7  " 

Height  of  shaft 12.0         "      =40" 

Total  height  of  furnace 13.7         "      =45  " 

These  Norway  furnaces  are  somewhat  different  from  the 
Trollhattan  furnace.  The  volume  of  the  shaft  is  smaller,  but 
its  diameter  is  greater  than  the  Corresponding  shaft  of  a  charcoal 
furnace.  The  coke  in  the  charge  gives  it  greater  conductivity, 
so  that  a  lower  voltage  is  used. 

The  ratio  of  volume  of  charge  per  day  to  shaft  volume  has 
been  taken  at  1.55,  and  the  furnace  volume  has  hence  been 


THE   ELECTRIC   SHAFT  FURNACE  253 

made  38  cubic  metres  (about  500  cu.  ft.).  The  furnace  hearth 
is  lined  with  magnesite.  The  general  contour  of  the  furnace 
walls  and  roof  over  the  hearth  can  best  be  seen  by  consulting 
Fig.  125.  The  roof  is  cooled  as  described  under  operating  costs. 
The  gas  that  is  blown  through  the  tuyeres  is  cleaned  in  a  water 
scrubber  in  the  latest  designs,  as  shown  in  Figs.  126  and  127. 
The  electrodes  used  during  the  beginning  of  1911  were  built 
up  of  4  carbons — 2  metres  (6^2  ft.)  long  and  330  x  330  mm. 
(13"  x  13")  section  arranged  to  form  an  electrode  660  x  660 
mm.  (675  sq.  in.)  section.  17,000  amps,  is  the  permissible 
maximum  or  25  amps,  per  sq.  in.  Toward  the  end  of  the  year 
this  has  been  changed  to  a  cylindrical  electrode  of  600  mm. 
(23.6  in.)  diameter,  which  is  gripped  much  shorter  than  formerly 
(see  Fig.  126),  thus  saving  40  kw.  The  square  electrodes  were 
supplied  by  both  the  Plania  Works  of  Ratibor,  Germany,  and 
from  the  Hoganas  Works,  Sweden.  The  600  mm.  round  elec- 
trodes have  lately  been  furnished  by  the  former  works  and  by 
Siemens  Bros.  &  Co.,  Litchenberg,  near  Berlin.  The  upper  part 
of  the  electrodes  is  covered  with  sheet  asbestos  and  thin  sheet- 
iron,  and  the  top  surface  is  covered  with  a  thick  layer  of  ground 
asbestos  and  silicate  of  potash.  They  also  have  a  water-jacket, 
beneath  which  gas  was  blown  to  cool  the  roof  (see  Fig.  124). 
This  practise  was  not  long  continued,  as  the  C02  burned  holes  in 
the  electrodes. 

WThen  starting  the  furnace,  it  is  thoroughly  dried  out  with 
wood  and  charcoal  fires,  and  heated  up  electrically  by  filling 
the  hearth  with  coke  and  turning  on  the  current.  About  3 
weeks  is  taken  to  burn  through  an  electrode  above  the  so-called 
"stock  line."  During  January,  1911,  the  average  voltage  on 
each  phase  was  62.6  volts,  and  the  average  current  per  phase 
14,449  amps.  The  average  reading  on  the  wattmeter  was  1535 
kw. ;  the  power  factor  was  consequently  .88  +  %.  The  efficiency 
of  the  furnace  has  been  greatly  increased  since  the  tests  were 
made  with  the  800  h.p.  furnace  at  Domnarfvet,  and  is  discussed 
under  operating  costs. 

The  following  table  indicates  the  efficiency  obtained  during 
the  tests  as  indicated: 


254  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


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THE   ELECTRIC  SHAFT  FURNACE  255 

Comparing  the  last  two  sets  of  figures  with  the  first  four  sets,  it 
will  be  seen  what  a  great  improvement  has  been  made  during 
1911.  Comparing  the  above  with  the  1909  tests  shown  on  page 
251,  the  improvement  deserves  the  recognition  it  has  received, 
in  that  over  60,000  h.p.  of  these  furnaces  have  since  been  built 
or  are  building. 

It  is  interesting  to  know  exactly  what  the  first  large  2500 
h.p.  furnace  installation  of  Gronwall,  Lindblad  &  Stalhane  cost 
at  Trollhattan,  which  has  a  daily  capacity  of  about  20  tons.  The 
furnace  house  is  of  steel  construction,  and  brick  and  both  furnace 
and  electric  equipment  cost  more  than  a  subsequent  similar 
installation  would,  as  this  was  the  first  one  of  this  size.  The 
cost  was  as  follows: 

Excavation,  railway  connection,  water-pipes,  scale,  etc.  $10,727 

Buildings:   Furnace  house 14.735 

Charcoal  storage-house 6,032 

Crusher-house,  office,  laboratory,  shops 3,96 1 

Furnace I3,m 

Electric  equipment 13.782 

Cable  and  wires 3,832 

Gas-motor,  pumps,  reservoir 3,222 

Crushers 1,011 

Transformers 3,433 

Motors  for  crushers,  etc i,724 

Laboratory  equipment,  furniture,  etc 10,430 


$86,000 


In  order  to  give  an  idea  as  to  the  size  of  the  necessary  plant, 
it  may  be  said  that  an  output  of  10.65  kg-  (23-45  lbs-J,  P61"  h-P- 
day  corresponds  to  a  power  consumption  of  1736  kw.  hrs.  per 
metric  ton.  With  a  daily  output  of  300  metric  tons  this  would 
need  about  35,000  h.p.  at  the  furnace,  or  about  38,500  h.p.  at 
the  power  station,  when  allowing  for  a  long  transmission  line. 
If  a  plant  is  built  for  $50.00  per  h.p.,  it  would  require  a  capital 
of  $1,925,000.  Allowing  9%  for  interest  and  amortization,  and 
3%  for  taxes,  etc.,  each  h.p.  year  would  cost  about  $6.00  at  the 
power  station,  or  about  $7.50  at  the  furnace. 

A  complete  furnace  installation  for  300  tons  would  cost 
about  $500,000  and  consist  of  six  furnaces  of  7,000  h.p.  each, 


256     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

one  furnace  remaining  in  reserve.  This  estimate  is  based  on 
the  installation  costs  already  obtained,  but  each  furnace  would 
be  larger. 

It  only  remains  to  mention  that  because  of  the  very  favorable 
results  obtained  at  Domnarfvet,  1909,  the  Jernkontoret  of  Stock- 
holm has  acquired  the  patents  of  Gronwall,  Lindblad  &  Stalhane. 
The  British  owners  of  these  patents  are  the  Electro  Metals, 
London,  whose  American  and  Canadian  representative  is 
American  Transmarine  Co.,  Inc.,  New  York. 

Iron  ore  reduction  or  electric  pig-iron  furnaces  of  different 
makes  are  built  or  building,  among  these  notably  some  in 
northern  Italy.  Fifteen  electric  shaft  furnaces  of  the  Gronwall, 
Lindblad  &  Stalhane  design  are  now  (1919)  operating  or  build- 
ing for  Sweden,  aggregating  60,000  Kw.  One  other  is  destined 
for  Aosta,  Italy,  and  one  of  these  of  3,000  Kw.  for  Japan.  All 
of  the  Swedish  furnaces  are  operating  with  charcoal,  although 
it  is  stated,  that  very  successful  trials  have  been  made  on  coke. 
The  latt^r's  price,  however,  is  at  present  too  high  to  consider 
its  use.  With  Swedish  magnetites  of  57  to  58%  iron,  the 
power  consumption  per  metric  ton  is  about  22,000  Kw.hr. 
With  50%  ore  it  increases  to  2,500  Kw.hr.  The  charcoal  con- 
sumption is  averaging  300  to  330  kg.  per  ton  of  pig-iron  made 
and  the  best  grade  of  carbon  electrode  averages  6  to  7  kg.  per 
ton  of  pig-iron  made 


CHAPTER   XV 

GENERAL   REVIEW 

IN  addition  to  the  methods  of  furnace  construction  previously 
described  there  are  naturally  a  tremendous  number  of  proposals 
for  the  design  of  electric  furnaces.  This  is  best  brought  out  by 
the  many  patents  that  have  been  issued  both  for  arc  and  induction 
furnaces.  Although  the  literature  of  such  patent  papers  may  be 
very  entertaining,  and  is  indeed  very  often  instructive,  yet  a 
consideration  of  the  many  proposals  does  not  lie  within  the 
scope  of  this  book. 

Most  of  them  are  only  proposals  and  will  never  be  tried  out. 
A  smaller  number  disappear  quickly  after  a  trial  and  leave  no 
trace,  while  the  third  and  smallest  part  stand  trial  in  one  or 
another  plant.  They  enable  the  saving  of  the  license  fee  for  a 
successful  furnace,  but  most  of  them  cost  enormous  sums  for 
experiments,  and  very  often  complications  develop  when  they 
are  put  in  operation. 

Although  they  are  not  for  the  most  part  of  value  to  many 
people  they  yet  have  the  advantage  that  they  help  to  spread  the 
knowledge  concerning  the  properties  of  electric  furnaces  further 
and  further.  On  the  other  hand,  it  is  naturally  only  through  a 
fresh  consideration  of  the  new  methods  of  construction  that  a 
further  perfecting  of  the  old  or  even  new  ways  can  be  found  for 
reaching  the  wished-for  goal. 

On  this  account,  therefore,  it  is  perhaps  justifiable  to  con- 
sider at  least  a  few  of  the  furnaces  differing  in  construction  from 
those  used  most  frequently  today.  Another  reason  is  that 
one  or  the  other  of  them  are  sometimes  discussed  in  the  technical 
literature. 

Under  the  heading  of  arc  furnaces  comes  first  that  of  Chapelet, 
which  is  in  use  at  the  plant  at  Allevard  (Isere).  It  is  shown  in 
Fig.  113.  We  see  that  the  current  flows  in  an  arc  to  the  bath 


258      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


from  a  hanging  regulated  carbon,  similarly  to  the  Girod  furnace. 
From  the  bath  it  goes  through  a  horizontal  channel  to  a  hanging 
cast-iron  electrode  that  touches  the  channel.  This  constitutes 
the  peculiarity  of  the  furnace.  It  is  not  apparent  that  this 
arrangement  offers  any  advantage  over  that  of  the  Girod  furnace. 
In  the  first  place  the  furnace  construction  is  much  more  difficult 
and  not  so  accessible  as  that  of  the  Girod.  Further  it  is  to  be 
feared  that  the  metal  in  the 
channel  between  the  outer 
electrode  and  the  bath  will 
force  up  the  furnace  bottom, 
except  that  part  which  is 
not  molten,  because  of  the 
influence  of  the  water  cool- 
ing used  for  the  iron  elec- 
trode. This  will  bring  about 
difficulties  in  maintaining 
the  lining,  since  repairs  to 
the  horizontal  channel  are 
scarcely  possible.  The  meth- 
od of  working  is  exactly 
the  same  as  that  of  the 
Girod  furnace,  that  is  to 
say,  that  heat  is  produced 
exclusively  by  the  arc,  the 

resistance  offered  to  the  current  by  the  molten   material  not 
being  of  any  noticeable  value. 

The  details  of  construction  offer  little  that  is  worthy  of 
attention.  Water  cooling  is  used  at  the  opening  in  the  furnace 
roof  for  the  entrance  of  the  carbon  electrode,  at  the  outer  iron 
electrode,  and  also  at  the  carbon  electrode  connections  where 
the  current  passes  from  the  copper  cables.  The  cylindrical 
furnace  roof  is  removable.  The  openings  in  the  front  part  of 
the  roof  are  used  as  working  doors,  as  shown  in  the  illustration. 
There  are  several  of  these  furnaces  in  Allevard,  but,  according  to 
Coussergues'  report,  only  one  is  in  operation. 

The  Keller  furnace,  shown  in  Fig.   114,  has  still  greater 


FIG.  113. 


GENERAL    REVIEW 


259 


similarity  to  the  Girod  furnace.  The  only  difference  is  a  special 
arrangement  of  the  bottom  electrodes.  While  Girod,  as  we  have 
seen,  uses  several  water-cooled  steel  electrodes  that  are  dis- 
tributed over  the  bottom  surface  of  the  hearth,  Keller  uses  a 
furnace  bottom  formed  of  a  so-called  mixed  conductor.  As 


FIG.  114. 


seen  in  the  illustration  this  bottom  consists  of  a  water-cooled 
iron  plate  over  the  whole  surface  of  which  are  set  a  number  of 
evenly  distributed  iron  rods  from  one  inch  to  1.18"  in  diameter, 
between  which  magnesite  is  rammed.  This  is,  in  itself,  a  fairly 
good  conductor.  In  this  way  a  semi-refractory  bottom  is  formed 


260      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

with  a  conduction  between  that  of  iron  and  magnesite.  Accord- 
ing to  Keller's  results  such  a  bottom  is  practically  unmel table. 
It  is  questionable  whether  his  electrode  arrangement  offers  any 
advantage  over  that  of  Girod.  It  depends  on  the  durability  of 
the  furnace  hearth  in  the  two  cases  concerning  which  only  work 
under  practically  the  same  conditions  can  give  conclusions.  The 
production  of  heat  in  the  two  furnaces  is  in  no  way  influenced 
by  the  bottom  electrodes.  The  uniform  composition  of  the 


FIG.  115. 

whole  furnace  bottom  in  the  case  of  the  Keller  furnace  will  not 
bring  about  the  profitable  circulation  of  the  bath  found  in  the 
Girod  furnace. 

In  this  case  also  the  original  Girod  is  to  be  preferred  to  the 
newer  Keller  furnace,  provided  that  the  bottom  will  last  as  long 
in  the  first  case  as  in  the  second. 

Often  one  finds  in  the  patent  papers  the  endeavor  to  increase 
the  resistance  of  the  bath  by  means  of  a  suitable  shape  of  hearth, 
and  so  bring  about  an  additional  resistance  heating.  As  an 
example,  the  Nathusius  furnace  may  be  mentioned.  Fig.  115 
gives  a  section  of  this  furnace  taken  from  the  patent  papers.  It 
shows  a  number  of  electrodes  of  changeable  polarity  arranged 


GENERAL    REVIEW 


261 


above  and  below  the  melted  material.  In  this  way  the  current 
can  be  forced  to  flow  through  and  around  the  molten  bath. 
According  to  the  description  given  with  the  drawing,  the  current 
flows  first  from  the  upper  middle  electrode  b  through  the  slag 
covering  h  and  the  upper  layers  of  the  metal  bath  to  the  upper 
outer  electrodes  a  and  c,  second  from  the  lower  middle  electrode 
e  to  the  lower  outer  electrodes  d  and  /.  In  addition,  however, 
the  current  ought  to  travel  from  the  outer  upper  electrodes  a 
and  c  to  the  outer  lower  steel  electrodes  d  and  f,  so  that  the  bath 
will  be  enclosed  by  heat-producing  currents. 

The  whole  arrangement,  as  is  immediately  apparent,  repre- 
sents a  combination  of  the  Heroult  and  Girod  furnaces.     In  the 


FIG.  116. 

first  place  it  is  presumed  that  it  is  possible  to  heat  the  bath  by 
current  led  in  through  electrodes  which  have  a  much  smaller 
section  than  that  of  the  bath.  This  is  naturally  altogether 
impossible  if  the  electrodes  consist  of  carbon,  as  is  the  case  with 
those  arranged  over  the  bath,  which  has  an  excessively  high 
resistance  in  comparison  with  the  fluid  metal.  In  addition  it 
can  be  shown  that  it  is  impossible  to  bring  about  much  heating 
by  means  of  the  water-cooled  electrodes,  for  their  section  in 
proportion  to  the  bath  is  so  small  that  the  higher  specific  resist- 
ance of  the  bath  can  have  no  important  influence.  Fig.  116 
shows  the  practical  arrangement  of  a  Nathusius  furnace  that 
differs  from  the  drawing  in  the  patent  papers  because  of  a 
simpler  and  therefore  better  form  of  hearth.  Here  a  direct 
heating  of  the  bath,  by  means  of  the  bottom  electrodes,  is  not 


262      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


FlG.  117. 


taken  into  consideration  because  of  the  greatly  increased  section. 
The  arrangement  of  the  water-cooled  electrodes  in  the  latest 
furnaces  differs  from  Fig.  115,  and  according  to  Neumann's 
report  in  Stahl  und  Risen,  1910,  they  have  a  diameter  of  8.66", 
and  are  covered  with  a  layer  of 
dolomite  7.87"  thick.  With  the 
passage  of  the  current  this  layer 
gives  off  heat,  and  so  much  as  is 
not  carried  away  through  the 
bottom  electrodes  enters  the  bath. 
For  increasing  this  bottom  heat- 
ing an  additional  150  kw.  trans- 
former is  used  for  a  5-ton  fur- 
nace. Currents  of  a  maximum  of 
6000  to  8000  amperes  are  used, 
that  enter  the  bath  frpm  each 
carbon  electrode,  when  a  three 
phase  no  volt  current  is  em- 
ployed amounting  to  about  2500 

amperes.  The  direct  heating  of  a  metal  bath  n.8"  deep  and 
about  78.74"  diameter  is  altogether  impossible  with  these 
currents.  It  is  therefore  also  im- 
possible with  the  present  arrange- 
ment of  the  furnace  to  use  the 
bottom  heating  alone,  although 
this  is  advanced  as  a  special  ad- 
vantage of  the  furnace  in  question. 
After  all,  the  small  advantage 
that  the  bottom  heating  may  bring 
about  must  be  looked  upon  as 
dearly  purchased  when  it  is  con- 
sidered that  the  Nathusius  furnace 

shows  a  much  more  complicated  construction  than  the  Heroult 
or  Girod  alone,  and  uses  practically  the  same  method  of  heat- 
ing. Moreover,  it  has  more  electrodes  than  the  simpler  older 
furnaces  and  therefore  has  greater  heat  losses.  In  addition 
six  conductors  are  used  for  the  current  as  compared  with  three 


FIG.  118. 


GENERAL    REVIEW 


263 


for  the  Heroult  furnace.  Apart  from  this  the  method  of  con- 
struction does  not  appear  as  good  as  that  of  either  the  Heroult 
or  Girod  furnaces. 

In  the  sphere  of  induction  furnaces  one  constant  endeavor 
appears  to  be  the  production  of  greater  movement  in  the  bath 
of  metal.  Most  of  the  proposals  show  an  ignorance  of  the 
principles  of  the  induction  furnace,  for  otherwise  the  designers 
would  know  that  in  these  furnaces  a  completely  satisfactory 
mixing  of  the  whole  molten  material  is  produced  by  the  electric 


FIG.  119. 

and  magnetic  conditions  themselves.  We  can,  therefore,  leave 
out  of  consideration  all  the  proposed  furnaces  that  make  use  of 
inclined  channels  of  small  section  through  which  the  hotter 
material  ought  to  rise,  while  the  colder  should  descend.  Such 
an  arrangement  proposed  by  Gin  is  shown  in  Fig.  117. 

The  Schneider-Creusot  induction  furnace,  of  which  a  section 
is  given  in  Fig.  118.  is  worthy  of  notice.  This  furnace,  however, 
has  not  been  improved  since  it  was  first  designed.  Like  the 
Gin  furnace  mentioned  above,  and  which  appeared  much  later, 
it  shows  an  induction  channel  with  several  hearth-like  widenings. 


264      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

All  such  constructions  of  induction  furnaces  have  the  disadvan- 
tage that  extremely  high  temperatures  must  be  produced  in  the 
narrow  channels  if  the  material  in  the  hearths  is  to  be  kept  hot 
enough.  This  brings  about  a  very  energetic  attack  on  the  lining 
at  these  places,  and  as  a  result  high  maintenance  costs  and 
frequent  delays  in  the  working  of  the  furnace  with  the  Schneider- 
Creusot  furnace  refining  is  only  carried  out  in  the  hearth  A ,  and 
the  remaining  metal  is  kept  free  from  slag.  The  use  of  the 
small  hearth  B  is  therefore  not  apparent.  The  arrangement 
of  the  furnace  cannot  be  called  simple.  With  this  furnace  also 
great  value  is  laid  on  the  increase  of  movement  in  the  bath  due 
to  the  great  differences  in  section,  and  this  appears  reasonable. 
For  obtaining  this  circulation  the  furnace  is  built  on  three 
columns,  two  of  which  allow  a  rise  or  fall  in  the  furnace,  so  that 
during  the  operation  the  heating  channels  or  pipes  can  be  in- 
clined at  a  sharp  angle. 

The  furnace  at  the  Creusot  Works  is  arranged  for  a  one- 
ton  charge. 

Other  types  of  induction  furnaces  endeavor  to  increase  the 
resistance  of  the  bath,  and  so  bring  about  an  improvement  in 
the  power  factor.  The  proposal  of  Gronwall,  which  is  shown  in 
Fig.  119,  may  serve  as  an  example.  We  see  here  the  ordinary 
channel  of  the  induction  furnace,  greatly  elongated  on  one  side. 
This  arrangement  naturally  brings  about  a  considerable  increase 
in  the  resistance  of  the  bath,  but  it  has  the  disadvantage  of 
causing  very  great  radiation  losses.  Further,  it  is  impossible, 
according  to  metallurgical  practise,  to  maintain  the  division 
wall  that  is  necessary  between  the  two  parallel  parts  of  the 
hearth,  because  no  refractory  material  is  known  that  will  resist 
an  intense  heating  from  both  sides.  Further,  it  may  be  men- 
tioned that  such  a  furnace  can  only  be  used  for  the  melting  of 
pure  materials,  for  work  with  slags  cannot  be  carried  out  even 
to  the  small  extent  possible  in  the  purely  ring-shaped  furnaces. 
This  proposal,  also,  has  not  yet  passed  the  experimental  stage. 

Roberston,  in  the  November,  1911,  issue  of  the  Metallurgical 
and  Chemical  Engineering,  writes  of  the  Gronwall  two  phase  arc 
furnace.  This  furnace  is  the  invention  of  Gronwall,  Lindblad 


GENERAL    REVIEW 


2G5 


&  Stalhane.  Having  originally  worked  with  various  types  of 
induction  furnaces  without  great  success  they  decided  to  design 
an  arc  furnace.  This  furnace  operates  with  two  phase  current, 
having  two  vertical  carbons  passing  through  the  roof,  each  one 
to  a  phase.  See  Fig.  i  iga.  The  current  arcs  from  the  electrodes 
to  the  charge,  passing  through  this  and  then  through  the  basic 
lining  at  the  centre  of  the  hearth  bottom,  to  the  neutral  return 
which  is  a  carbon  block  fixed  in  the  bottom  of  the  furnace.  The 

top  of  this  bottom  electrode 
comes  level  with  the  brick- 
work so  that  it  does  not 
project  into  or  in  any  way 
weaken  the  basic  lining. 
The  hearth  of  the  furnace 
therefore  is  not  broken  by 
any  projections.  The  fur- 
nace has  three  doors,  one  at 
each  end  and  one  at  the 
spout.  Either  hand  or 
FlG  II90  automatic  regulation  is  pro- 

vided for   the    electrodes. 

This  furnace  is  of  the  tilting  variety,  being  mounted  in  curved 
rails.  Heat  regulation  is  obtained  by  varying  the  voltage  of  a 
special  regulating  transformer.  The  normal  working  voltage 
is  55,  no  and  220  and  10%  tap  voltages. 

As  each  phase  of  a  two  phase  circuit  is  connected  to  one  of 
the  vertical  electrodes  the  arcs  are  independently  formed,  so  that 
if  one  arc  is  broken  the  other  remains.  This  insures  steadier 
running  than  if  both  arcs  were  in  series  as  in  the  Heroult  furnace. 
The  arrangement  of  two  arcs  operating  in  parallel  with  a  neutral 
return  through  the  bottom  produces  a  vertical  as  well  as  a 
horizontal  circulation  in  the  metal  bath,  slightly  different  from 
that  in  a  Girod  furnace. 

The  Greaves-Etchells  electric  furnace  is  described  by  the 
inventors  as  being  of  the  arc  resistance  type,  and  that  it  com- 
bines the  advantages  of  both  direct  arc  and  resistance  heating. 
It  was  first  introduced  by  two  engineers  and  metallurgists, 


266     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY ' 

Greaves  and  Etchells,  of  Sheffield,  England,  in  1915.  It  was 
the  aim  of  the  inventors  to  produce  a  furnace  which  would  fill 
the  following  conditions: 

1.  A  system  which  should  be  applicable  to  any  polyphase 
supply  system,  especially  those  of  high  frequency,  and  which 
should  maintain  a  steadier  phase  balance,  and  higher  power 
factor. 

2.  The  generation  of  heat  in  such  a  manner  that  it  was  ap- 
plied as  directly  as  possible  to  the  metal  in  the  furnace,  and  did 
not  superheat  the  slag  and  various  portions  of  the  lining  more 
than    was  essential  to  maintain  the  metallurgical  conditions 
necessary  for  refining  steel. 

3.  Rapid  melting  and  uniform  heating  of  the  charge. 

4.  Automatic  circulation  of  metal — giving  uniform  quality  of 
steel — and  avoiding  use  of  stirrers  and  rabbling. 

5.  The  construction  of  the  furnace,  which  should  be  free 
from  obvious  mechanical  defects. 

In  order  to  obtain  an  even  temperature  through  the  bath  of 
molten  metal  in  the  electric  furnace,  the  inventors  believe  that 
heat  must  be  applied  below,  as  well  as  above,  the  bath.  In 
order  to  effect  this,  the  hearth  of  the  furnace  is  specially  con- 
structed. 

The  hearth  lining  is  never  less  than  500  millimeters  (20 
inches)  thick,  and  is  constructed  mainly  of  dolomite,  magnesite, 
and  other  materials,  in  such  a  manner  that  it  is  believed  the 
electrical  resistance  is  high  at  the  inside  of  the  bath  in  proximity 
to  the  charge  and  decreases  rapidly  to  a  negligent  quantity 
at  the  outside.  (The  details  of  the  bottom  construction  are  not 
divulged.) 

Two  phases  of  the  3-phase  low-tension  supply  are  connected 
to  their  respective  upper  graphite  or  carbon  electrodes  while 
the  third  phase  is  connected  to  the  bottom  of  the  hearth.  The 
charge  thus  lies  between  the  three  sources  of  power.  The 
current  flowing  through  the  bath  generates  some  heat  immedi- 
ately below  the  liquid  (see  page  155  for  similar  cases),  while 
electric  arcs  arranged  over  the  bath  maintain  the  slag  and  surface 
at  the  desired  temperature. 


GENERAL   REVIEW 


207 


We  quote  again  from  the  inventors, "  The  effect  of  this  bottom 
heating  is  to  cause  'convection  currents'  in  the  molten  metal, 
which  ensure  a  constant  circulation  of  a  uniform  product.  The 
outside  of  the  furnace  bottom  remains  cold,  little  or  no  heat 
being  lost  in  this  direction." 

The  system  of  transformer  ratios  is  arranged  so  as  to  give  a 
perfect  balance  when  the  upper  electrodes  are  in  equal  adjust- 
ment.      The     high  -  tension 
electric  supply  is  transformed 
by   means    of    a    delta-star 
connection  (see  Fig.  IIQ&). 

The  transformer  connec- 
tions are  such  that  the  short- 
circuit  current  of  one  elec- 
trode must  traverse  two 
transformers  in  series  and 
in  different  phase,  which 
automatically  lowers  the 
power  factor  momentarily, 
and  has  a  cushion  effect; 
the  fact  that  there  is  always 
a  permanent  resistance  in  FIG.  119  b. 

the    path     of     the    current 

through  the  hearth  also  limits  the  effect  of  the  short  circuits. 
The  combination  of  these  factors  provides  another  means 
devised  for  protecting  the  electrical  system  from  shock, 
while  allowing  a  high-power  factor  to  be  obtained  on  normal 
load,  which  averages  90  to  94%.  Automatic  electrode  regula- 
tors maintain  the  current  at  predetermined  figures.  Motor 
and  hand  regulation  are  also  provided.  Arrangements  are  pro- 
vided for  varying  the  voltages  across  the  arcs  and  the  ratio  of 
heat  generated  above  and  below  can  be  regulated  over  a  wide 
range.  The  doors,  of  special  construction  and  design,  effectively 
exclude  air  when  closed  and  prevent  loss  of  heat. 

The  furnaces  are  constructed  in  various  sizes,  from  J^  to 
30  tons,  the  largest  one  in  operation  now  is  taking  15  tons  of 
cold  metal. 


268     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Fig.  ngc  shows  the  general  design  of  the  furnace  of  the  3- 
to  30-ton  size.  They  are  mounted  on  rockers  operated  by  an 
electric  motor  at  the  rear  of  the  furnace.  There  are  teaming 
and  slagging  spouts  and  a  charging  door.  (See  Fig.  ngc.} 

The  mechanically  operated  electrodes  are  carried  by  separate 
jib  arms  to  winch  control.  The  whole  hearth  of  the  furnace  is 
connected  to  a  third  transformer  winding;  the  three  transformer 

windings  are  arranged 
in  star  while  the  pri- 
maries are  in  delta. 
The  bottom  electrode  of 
the  furnace  is  also  con- 
nected to  ground,  so 
that  the  star  point  of 
the  transformer  group 
is  above  the  earth  po- 
tential. As  shown  by 
the  figure,  the  3-ton 
furnaces  and  larger  are 
now  operated  with  four 
electrodes. 


FIG.  ngc. 


Diagrammatically  the  electrical  equipment  is  equivalent  to 
two  individual  parts  of  a  smaller  furnace.  Each  pair  of  electrodes 
with  their  respective  transformers  can  be  switched  individually, 
enabling  one  pair  of  electrodes  to  be  kept  in  operation  while 
adjustments  are  made  on  the  other  pair.  The  total  overload 
of  the  furnace  is  limited  somewhat  by  this  device,  because  each 
half  of  the  furnace  trips  its  particular  switch  when  its  own 
pair  of  electrodes  becomes  overloaded. 

It  is  claimed  that  due  to  "convection  currents,"  already 
mentioned,  there  is  a  very  rapid  refining  because  the  "mov- 
ing stream  of  metal  carries  away  the  intense  heat  of  the 
arcs,  bringing  all  parts  of  the  bath  in  contact  with  the 
refining  slags."  With  basic  linings,  a  3-ton  furnace  equipped 
with  900  KVA  transformer  capacity  is  melting  and  refin- 
ing 3  tons  of  steel  in  2%  hours.  Six-ton  furnaces  are 
melting  and  completing  heats  in  less  than  4  hours  per 


GENERAL    REVIEW 


269 


charge.  With  acid-lined  bottoms  these  figures  have  been 
improved. 

It  is  stated  by  a  company  operating  this  type  of  furnace  and 
another  arc  furnace  of  prominent  make,  that  "the  average 
kw.-hr.  consumption  per  ton  of  steel  produced  in  the  furnace 
(a  3-ton  Greaves-Etchells)  is  comparable  to  the  performance 
secured  in  a  6-ton  of  the  other  make." 

The  makers  of  the  Greaves-Etchells  electric  furnace  are  the 
Electric  Furnace  Construction 
Co.,  of  Philadelphia,  Pa.,  and 
T.  H.  Watson   &    Co.,  Ltd., 
Sheffield,  England. 

An  adaptation  of  the  orig- 
inal (1878)  Siemens  single- 
phase  bottom  electrode  type 
of  furnace  has  reappeared  for 
a  brief  time  in  a  form  known 
as  the  Snyder.  This  furnace 
has  a  unique  type  of  plug  door, 
shown  in  the  cut,  see  Fig.  119^. 
It  is  very  tight,  but  has  the 
disadvantage  of  not  being 
able  to  rabble  off  slag  without 

opening  the  entire  door.  The  furnace  uses  a  graphite  electrode 
— 4  diameter  for  a  i-ton  using  600  KVA,  at  60%  power 
factor — about  120  to  150  volts  at  the  arc;  the  density 
per  square  inch  is  high,  but  as  long  as  the  furnace  is  kept 
very  tight  during  operation,  the  graphite  electrode  con- 
sumption is  below  6  Ib.  per  net  ton  of  metal  melted  and  poured 
from  an  acid  bottom,  as  the  majority  of  these  furnaces  are 
operated.  Owing  to  the  very  high  power  employed  quick  heats 
are  possible  with  acid  refractories  throughout,  less  than  550 
kw.-hrs  for  2,000  Ib.  (910  kg.)  being  common. 

With  continuous  operation  10  heats  have  been  made  in 
24  hours  when  merely  melting,  "killing"  and  pouring.  One 
furnace  operating  basic,  making  ingot  steel,  now  makes  6  heats 
in  24  hours,  but  has  made  7,  also  8,  but  at  the  great  expense  of 


270     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


the  brick  work.     Owing  to  the  unpopular  single  phase  with  the 
central  station  managers,  together  with  the  low  power  factor, 


FIG.  1 190. 

60%,  and  the  difficulty  always  present  of  burning  out  the  bot- 
tom electrode,  not  to  mention  the  most  violent  electrical  surges, 
always  present,  this 
type  of  furnace  gradu- 
ally, again,  took  itself 
off  the  market,  in  the 
steel  industry. 

Following  this 
single -phase  furnace 
came  the  polyphase 
Snyder  operating  2- 
phase  3-wire  with  a 
bottom  contact.  (See 
Fig.  age.)  Com- 
pared to  the  contents 
of  the  furnace  the  steel 
water-cooled  part  of  the  contact  with  the  bath,  which  protrudes 


GENERAL   REVIEW  271 

through  the  refractory  bottom,  is  not  only  above  the  bottom 
but  external  to  it.  Copper  cables  going  to  this  bottom  contact 
are  therefore  no  longer  under  the  furnace  but  one  side  instead. 

Another  feature  of  this  furnace  is  a  hinged  roof  which  can 
be  swung  back  quickly  for  an  equally  quick  charging  from  a 


FIG.  ii9g. 

specially  designed  bucket.  This  latest  design,  as  can  be  seen 
from  Fig.  iiqf,  has  but  one  set  of  parts  for  tilting  the  furnace, 
and  also  the  roof  when  it  is  slid  back  for  charging;  see  also 
Fig.  upg. 

An  interesting  thing  which  has  been  tried  by  a  user  of  this 
furnace  is  the  preheating  of  the  steel  scrap  to  about  an  annealing 
temperature,  the  metal  being  charged  while  it  is  still  in  its 
solid  condition.  This  necessitated  94.6  liters  (25  U.  S.  gallons) 
of  fuel  oil  and  saved  180  kw.-hrs.  per  metric  ton  with  an  acid- 


272       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

lined  furnace.  Even  if  the  combined  cost  of  the  fuel  oil  and 
handling  is  the  same  as  electricity  saved,  the  process  is  eco- 
nomical, as  it  increases  the  output  about  40%  and  cuts  the 
time  per  heat  down  to  a  little  over  an  hour.  Besides  this,  it 
lessens  the  electrode  consumption,  the  refractory  and  repair 
cost  per  ton  of  output.  It  will  be  interesting  to  know  later  on 
what  the  saving  is  with  a  similar  method  with  a  basic-lined 
furnace.  Such  preheating  as  this  was  long  ago  proposed  by 
Professor  Joseph  W.  Richards,  but  this  is  the  first  instance  we 
know  of  where  it  has  been  used  in  conjunction  with  an  electric 
furnace;  and  with  the  constantly  rising  price  of  electricity  in 
certain  sections,  it  is  expected  that  this  economical  method 
will  come  into  being  more  and  more,  especially  considering  the 
small  outlay  for  preheating  the  scrap  to  be  charged. 

The  Greene  arc  furnace  made  its  appearance  on  the  Pacific 
Coast  during  the  Great  War.  Those  built  so  far  have  a  steel 
bottom  electrode  and  upper  carbon  or  graphite  electrode.  In 
principle  the  furnace  is  therefore  of  the  original  Siemens  type. 

Some  later  models  operate  with  2-phase  current,  also  hav- 
ing a  steel  bottom  contact  and  two  top  electrodes  of  carbon 
coming  vertically  through  the  roof. 

The  latest  models  are  also  built  in  the  shape  of  a  barrel 
lying  on  its  side;  in  form,  much  like  an  earlier  Rennerfelt  model. 
The  electrodes  are  regulated  only  by  hand,  so  far,  although 
automatic  electrode  control  can  be  attached.  The  furnace 
has  been  made  from  y^  to  2^-ton  sizes  per  heat,  and  is  often- 
times operated  with  an  acid  bottom. 

The  statistics  of  this  furnace  can  be  seen  on  another  page. 
It  is  handled  by  the  Greene  Electric  Furnace  Co.,  of  Seattle, 
Washington. 

Naturally  there  have  been  many  attempts  to  combine  the 
various  types,  such  as  the  induction  and  arc  furnace.  Fig.  120 
shows  one,  and  is  that  of  Hiorth.  (Such  proposals  originated 
at  the  time  when  the  causes  for  the  failure  of  the  channel-shaped 
induction  furnaces  for  refining  purposes  were  not  clearly  known, 
and  it  was  thought  that  the  slag  temperature  was  not  high 
enough.  In  the  meantime  the  successful  operation  of  the  Roch- 


GENERAL    REVIEW 


273 


FIG.  1 20. 


ling-Rodenhauser  furnaces  has  shown  the  incorrectness  of  this 
reasoning.)  In  Fig.  120  we  see  the  channel  of  an  induction  fur- 
nace broken  by  a  division  wall,  which  is  bridged  by  a  stirrup- 
shaped  electrode.  This  electrode 
should  only  just  touch  in  the  slag, 
and  bring  it  to  a  very  high  tempera- 
ture. This  shows  a  complete  ignor- 
ance of  the  probabilities.  The  un- 
mistakable result  of  the  proposed 
method  of  working  would  be  a  com- 
plete freezing  up  of  the  metal  in 
the  channel  on  the  opposite  sides 
of  the  electrodes.  It  would  be  im- 
possible to  introduce  sufficient  cur- 
rent into  the  bath  through  the  elec- 
trode with  which  to  produce  heat 
enough,  by  overcoming  the  bath  re- 
sistance, to  keep  the  metal  fluid. 

Even  so,  Hiorth  says  that  he  does  not  consider  this  furnace 
construction  to  be  valueless,  still  we  do  not  find  that  he  has 

used  this  method  in  the  single 
commercial  furnace  which  he 
has  constructed,  which  is  shown 
in  side  elevation  by  Fig.  121. 
This  is  a  purely  induction  type 
of  furnace  with  the  primary 
winding  in  flat  spools  similar  to 
the  arrangement  already  pro- 
posed by  de  Ferranti  and  later 
again  by  Frick,  excepting  that 
Hiorth  coils  both  legs  of  the 
magnet.  The  coils,  according  to 
a  paper  read  by  Dr.  Joseph  W. 

Richards  before  the  American  Electrochemical  Society,  in 
1910,  are  uninsulated  copper  coils,  hollow,  and  the  lower  ones 
water-cooled.  The  construction  of  the  furnace  is  such  that  it 
may  be  tilted  independently  of  the  magnet. 


FIG.  121. 


274    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

So  far,  Richards  continues,  Hiorth  uses  his  furnace  only  for 
melting  the  purest  obtainable  Swedish  Dannemora  pig-iron  and 
Dannemora  Walloon  iron.  Yellowish-white  blast-furnace  slag 
was  being  used  as  a  flux.  The  contents  of  the  furnace  being 
5  tons,  3  tons  were  poured  at  a  time  and  2  tons  left  in  to  start  the 
next  charge.  The  details  of  a  heat  run-off  are  then  given,  which 
are  here  omitted.  We  quote  further: 

"Assuming  300  calories  necessary  to  melt  i  kg.  of  steel,  the 
thermal  efficiency  of  this  melting  operation  is  55%  and  the 
furnace  radiation  loss  calculates  out  180  kw.  at  this  temperature. 


FIG.  121  a. 

It  was  stated  that  it  took  about  170  kw.  to  keep  the  charge 
melted  when  the  furnace  was  kept  up  to  heat  overnight." 

The  power  factor  varied  from  .80  at  the  beginning  of  the 
run  to  .57%  at  the  end,  when  the  metal  in  furnace  was  5.77  tons 
and  at  casting  temperature.  Current  used  averaged  395  kw. 
for  6  hours,  or  790  kw.-hrs.  per  ton  of  steel.  As  low  as  700 
kw.-hrs.  has  been  reached  in  this  5-ton  furnace  on  cold  mate- 
rials. This  furnace  operates  at  i2>£  cycles,  400  to  500  kw.  at 
250  volts  single  phase. 

The  Moore  electric  furnace  made  its  appearance  during  1917. 
It  is  a  3 -phase  arc  furnace  having  3  vertical  electrodes  set  in  the 
form  of  an  equilateral  triangle,  placed  symmetrically  over  a 
circular  hearth,  at  first  glance  resembling  the  Heroult  furnace. 
(See  Fig.  1216.) 


GENERAL  REVIEW 


275 


It  differs  in  its  electrical  connections  somewhat,  as  these  are 
arranged,  according  to  the  inventor,  "so  as  to  allow  an  adjustable 
amount  of  power  to  be  carried  to  the  charge  through  the  furnace 
bottom :  an  amount  of  power  sufficient  to  produce  a  circulation 
and  stirring  of  the  bath,  resulting  in  a  more  rapid  refining  of  the 
steel  and  better  mixing  of  alloys;  at  the  same  time,  the  amount 
of  power  transmitted  through  the  bottom  is  limited  in  such  a 


FIG.  121  b. 

manner  as  not  to  in  any  way  injure  or  shorten  the  life  of  the 
bottom." 

Fig.  1 210  shows  the  low- tension  switch  which  is  closed  when 
it  is  desired  to  have  the  current  flowing  through  the  bottom. 
By  means  of  a  multiplicity  of  series,  parallel  and  delta-star 
connections  a  number  of  voltages  can  be  produced  at  the  arc. 
This  causes  a  rather  elaborate  system  of  high-tension  wiring 
in  the  transformer  room.  The  bottom  switch,  letting  current 
flow  through  the  conducting  hearth,  is  not  always  closed, 
especially  not  with  acid  bottoms,  as  these  are  not,  as  is  well 
known,  nearly  so  good  an  electrical  conductor,  when  white 
hot,  as  are  the  basic  hearth  refractories.  The  bottom,  or  so- 
called  neutral  connection,  "permits  each  electrode  to  obtain 


276    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


contact  immediately  upon  its  touching  the  charge."    This  is  of 
course  after  the  basic  bottom  is  once  thoroughly  hot. 

The  furnace  is  more  highly  powered  than  some  other  furnaces, 
i.e.,  1000  KVA  at  40°  C.  rise  in  transformers  for  a  3-ton  furnace 
is  an  example.  It  has  a  wide  backward  tilting  angle,  allowing 
the  slag  to  be  removed  easily.  Special  attention  has  been  paid 
to  the  ready  renewal  of  the  refractories.  Records  of  the  3 -ton 
acid-bottom  furnaces  have  been  established  at  700  metric  tons 
per  month,  and  a  roof  lining  for  300  heats,  the  average  kw.-hrs. 
consumption  being  560  kw.-hrs.  for  a  "net  ton"  (908  kg.), 
equalling  616  kw.-hrs.  per  metric  ton. 

Either  graphite  or  carbon  electrodes  can  be  used.  For 
making  ingot  steel  the  furnace  is  operated  basic.  Automatic 
electrode  regulation  is  furnished  on  all  but  the  smallest  furnaces. 
It  is  made  in  i>^-,  3-,  6-,  and  1 2-ton  sizes,  and  smaller  ones  when 
desired.  Fig.  1216  shows  a  3-ton  furnace. 

This  furnace  is  handled  by  the  Pittsburg  Furnace  Co., 
Milwaukee,  Wisconsin. 

The  Booth-Hall  arc  furnace  also  made  its  appearance  during 
the  war  just  passed.  It  belongs  to  those  having  a  conducting 
refractory  hearth,  when  conditions  permit,  with  a  basic  bottom, 

and,  when  operating  with  an 
acid  bottom,  which  only  be- 
comes conducting  to  elec- 
tricity with  difficulty,  re- 
course is  had  to  an  auxiliary 
electrode,  making  three  in 
all  for  a  2 -phase  2 -wire 
system.  The  electrical  con- 
nection is  as  shown  by  Fig. 
1 2 ic.  Until  the  basic  bottom 
becomes  conducting,  the  third  or  auxiliary  electrode,  shown  by 
black  circle  in  Fig.  121  d,  is  always  used  anywhere  up  to  45 
minutes  per  heat,  depending  upon  the  conditions.  Great 
stress  is  laid  by  the  inventors  on  the  thorough  mixing  of  the 
metal,  due  to  the  cross  current  in  the  bath  during  the  latter 
part  of  a  basic  heat  when  the  hearth  becomes  conducting. 


FIG.  121  c. 


GENERAL    REVIEW 


277 


This  "mixing  action,"  so  called,  is  claimed  to  be  "very  beneficial 
in  refining  work,  producing  a  more  uniform  steel,  and,  if  alloy 
steels  are  to  be  made,  largely  prevents  segregation." 

In  the  light  of  this  claim,  it  must  not  be  forgotten  that  by 
far  the  greater  majority  of  quality  and 
other  electric  steels  to-day  are  made  with 
electric  furnaces  having  a  solid  and  not  a 
conducting  bottom,  and  it  has  yet  to  be 
shown  that  any  poor  steel  is  made  in  electric 
arc  furnaces,  just  because  the  bottoms  are 
solid  and  the  currents  passing  through  the 
bath  only  go  through  the  upper  portion  per- 
haps, instead  of  diagonally  through  the  molten 
steel  from  the  arc,  and  thus  through  the  refractory  bottom  and 
out.  Fig.  121  e  shows  a  3-ton  Booth-Hall  furnace. 


FIG.  121  e. 


278    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Furthermore,  it  is  to  be  remembered  that  with  an  acid-bot- 
tom furnace  of  this  type,  when  a  bottom  is  practically  non- 
conducting and  consequently  no  cross  currents  in  the  molten 
bath,  good  steel  is  made  nevertheless  with  selected  scrap,  and 
the  inventors  by  no  means  admit  that  their  acid  steel  is  inferior 
to  their  basic! 

When  operating  acid  with  the  auxiliary  electrode,  this 
latter  is  supposed  to  be  either  touching  the  cold  scrap  or  dip- 
ping in  the  slag  all  the  time,  so  that  no  arc  results  from  this 
electrode,  and  hence  the  two  arcs  are  not  in  series.  There  is  no 
particular  technical  advantage  in  this,  but  it  avoids  patent 
interference. 

One  of  these  furnaces  of  1.18  metric  tons  (2600  Ibs.  avoirdu- 
pois), having  600  KVA  in  transformers  behind  it,  is  making 
heats  on  a  basic  bottom  without  any  particular  effort  at  re- 
fining, and  when  melting  steel  scrap  regularly,  in  two  hours 
is  averaging  600  kw.  hrs.  for  .908  metric  tons  (2000  Ibs.),  cor- 
responding to  660  kw.  hrs.  per  metric  ton.  This  was  made  over 
a  one-month  period,  allowing  for  shut-downs  at  night.  Details 
of  this  are  given  hereunder,  and  also  of  the  3-ton  basic  furnace 
of  this  type  having  1200  KVA  feeding  it. 

OPERATION  OF  BOOTH-HALL  BASIC  BOTTOM  FURNACE 
1.18  Kg.  (2600  Lbs.)  Capacity — 600  KVA — February,  1919 

Total  number  of  heats : 1 16 

Total  working  [days 27 

Average  heats  per  working  day 4.3 

Total  charge  (Ibs.,  294,640)  (kg.) 133,400 

Average  charge  per  heat  (Ibs.,    2540)  (kg.) 1,150 

Total  charge  (net  tons,  147.3)  metric  tons 133-4 

Average  daily  output  (net  tons,  5.45)  metric  tons 4.95 

Total  kilowatt  hours 88,330 

Average  kilowatt  hours  (per  net  ton,  2000  Ibs.  avoirdupois  =  600) 

metric  tons 660 

Total  charging  time  (minutes) 2,944 

Average  charging  time  per  heat  (minutes) 25 

Total  melting  time  (minutes) 13,688 

Average  melting  time  per  heat  (minutes) 118 

Total  pouring  time  (minutes) 2,320 

Average  pouring  time  per  heat  (minutes) 20 


GENERAL   REVIEW 


279 


OPERATION  OF  BOOTH-HALL  BASIC  BOTTOM  FURNACE 
3-Ton  Capacity — 1200  KVA 


ANALYSIS 

Time 
of  Heat 

Charge 
Lbs. 

Kg. 

Total 
Power 
KWH. 

Power 
per  Ton 
KWH. 

Heat 

No. 

C. 

Mn. 

Si. 

P.    S. 

427 

.24 

•56 

30 

Under  .05 

Hrs.  Min. 

-55 

6000 

2722 

1640 

Net 

547 

Metric 
603 

428 

.20 

.70 

-30 

Under  .05 

-45 

6000 

2722 

1500 

500 

550 

432 

.29 

.60 

•35 

Under  .05 

2-00 

6000 

2722 

1700 

567 

625 

433 

•31 

.67 

.28 

Under  .05 

-50 

6000 

2722 

1460 

487 

537 

434 

•30 

.60 

.22 

Under  .05 

-50 

6000 

2722 

I52O 

507 

558 

437 

.24 

-56 

•32 

Under  .05 

2-05 

6000 

2722 

I6OO 

533 

588 

438 

.22 

.61 

.28 

Under  .05 

-35 

5000 

2268 

1340 

536 

592 

439 

•23 

•54 

•29 

Under  .05 

-55 

6000 

2722 

1450 

483 

533 

440 

.27 

-59 

•30 

Under  .05 

-20 

4000 

1815 

II2O 

56o 

617 

An  electric  steel  furnace  of  new  design,  which  has  recently 
been  put  in  operation,  has  certain  features  which  distinguish  it 
from  some  of  the  more  familiar  types.  The  furnace  is  known 
as  the  Vom  Baur  electric  furnace. 

A  6;ton  unit  of  this  new  furnace  was  started  in  February,  1919, 
since  which  time  others  have  followed  both  here  and  abroad. 

It  seems  that  very  soon  after  electric  furnaces  in  the  iron 
and  steel  industry  were  placed  in  commercial  operation  in  the 
United  States,  some  thirteen  years  ago,  it  became  evident  that 
one  of  the  limits  of  its  possibilities  depended  on  the  life  of  the  re- 
fractories. All  kinds  and  types  of  electric  furnaces  have  to  take 
care  of  this  item  much  more  than  any  open-hearth  furnace. 
The  experience  of  many  electric  furnace  operators  and  designers 
has  been  of  this  nature.  The  simplest  refractories  of  any  arc 
furnace  are  those  of  the  single  phase,  single  electrode  type, 
with  a  bottom  electrode,  when  this  has  a  round  hearth  and  the 
carbon  electrode  at  its  center.  It  is  evident  that  the  heat  at 
the  inner  contour  of  the  side  walls  and  of  the  slag  line  of  this 
furnace  is  the  same  at  any  point  thereof.  Consequently,  when 
the  side  walls  burn  away,  they  do  so  equally.  That  is  to  say, 
there  are  no  hot  spots  on  any  portion  of  the  side  walls  or  slag 
line,  due  to  the  heat  of  the  arc,  and  manifestly  no  portions  of  the 
refractories  need  repairs,  when  properly  laid,  prior  to  some  other 
portion.  As  the  single-phase  furnace  of  any  but  the  smallest 


280      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

sizes  is  not  popular  with  central  station  managers,  it  is  seldom 
seen  to-day  in  the  newer  installations,  polyphase  furnaces  hav- 
ing almost  exclusively  taken  their  place. 

At  first,  on  account  of  the  many  advantages  of  the  polyphase 
furnace,  compared  to  the  single-phase,  the  refractory  feature  as 
above-  mentioned  did  not  receive  the  attention  it  deserved  until 
the  appearance  of  the  Vom  Baur  electric  furnace,  which  has, 
with  its  three  electrodes,  3-phase  3-wire,  or  2-phase  3-wire,  the 
same  good  heat  distribution  as  the  simple  single-phase  furnace. 


FIG.  121  f. 

This  good  heat  distribution  in  the  Vom  Baur  furnace  is  ac- 
complished by  the  combination  of  placing  three  electrodes  in  a 
straight  line.  The  contour  of  the  inner  refractories  can  easily 
be  ascertained  so  as  to  give  a  curve  to  the  refractories  which 
is  correct,  so  that  the  heat  at  the  slag  line,  at  the  side  walls, 
and  at  the  hearth  banks  is  the  same,  thus  assuring  among  others 
the  equal  burning  away  of  all  the  refractories  involved.  Only 
very  small  allowances  from  the  theoretical  have  to  be  made 
in  order  to  accomplish  this  purpose. 

The  shape  given  to  these  furnaces  is  shown  by  the  illustra- 
tion, Fig.  1 2 1/.  This  shows  a  well-defined  minor  axis  drawn 
through  the  middle  electrode,  and  this  shape  is  the  natural 


GENERAL   REVIEW  281 

result  of  the  radiated  heat  reaching  points  on  the  minor  axis 
from  the  three  electrodes.  With  2-phase  theoretically  the 
central  electrode  would  have  41%  more  heat  than  either  of  the 
end  electrodes,  but  it  .is  not  possible  to  reach  this  condition 
practically  and  maintain  the  arcs  at  their  best  setting.  The 
current  at  the  central  electrode  is  therefore  diminished  by  sev- 
eral per  cent.  Even  so,  the  heat  from  the  central  arc  is  more 
on  an  average  than  from  either  of  the  end  arcs  and,  consequently, 
in  order  to  keep  the  refractories  at  their  proper  distances,  the 
metal  bath  has  a  larger  surface  than  the  furnace  would  have  if 
each  of  the  electrodes  ever  gave  off  an  equal  amount  of  heat. 
It  is  well  here  to  quote  Ryan  (American  Foundrymen's  Associa- 
tion, October,  1918),  where  he  says:  "The  ideal  furnace  is  one 
which  exposes  the  largest  possible  surface  of  the  metal  to  the 
action  of  the  slag  without  being  subject  to  freezing  conditions  at 
any  part  of  the  furnace."  With  basic  operation  the  advantage 
is  that  the  metal  presents  a  greater  slag  area  for  the  same  tonnage. 
As  the  rate  of  refining  depends  not  only  on  the  chemical  com- 
position of  the  slag,  the  heat  at  the  point  of  contact  between 
the  metal  and  the  slag,  but  also  on  the  amount  of  surface  en- 
gaged between  the  slag  and  the  metal,  it  follows  that  the  rate 
of  refining  is  quicker. 

There  is  very  little  poking  to  be  done  in  this  furnace  when 
melting  down  cold  scrap,  as  there  are  no  hot  or  cold  spots  on 
the  side  walls  or  near  the  doors.  The  quick  melting  down  with 
this  furnace,  as  with  all  others,  depends  mostly  on  the  amount  of 
transformer  capacity  which  the  furnace  has.  However,  as  this 
furnace  has  an  even  heat  distribution  at  the  side  wall  refrac- 
tories, it  is  more  efficient  than  the  other  furnaces  which  lack 
this  feature.  Special  attention  has  been  given  to  the  doors, 
which  have  water-cooled  frames,  and  which  fit  very  snugly, 
allowing  for  all  expansion,  and  yet  can  be  tightened  after  they 
are  closed  by  giving  a  few  turns  to  two  handles. 

Structurally  the  furnace  is  strong,  having  a  rounded  and 
cone-shaped  bottom  connected  with  the  upper  shell,  which  is  a 
series  of  curves.  This  sets  on  two  rocker  arms  and  the  whole 
is  tilted  by  means  of  connecting  rods  from  suitably  geared 


282   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

mechanism  in  such  a  way  that  when  the  furnace  has  reached  its 
maximum  tilting  position  and  the  operating  motor  should  con- 
tinue to  run  for  any  reason,  the  furnace  goes  back  to  its  normal 
position.  The  tilting  mechanism  also  allows  the  furnace  to 
tilt  slightly  backwards  some  6  and  7  degrees  so  that  the  slag 
can  be  taken  off  at  this  door  instead  of  from  the  spout.  Both 
doors  are  used  for  charging.  See  Fig.  12  ig. 

The  center  of  gravity  of  the  furnace  is  low,  as  the  heavy 
part  of  the  standards  is  no  higher  than  is  needed  for  the  full 
travel  of  the  arm  holding  the  electrodes,  and  as  these  have  an 
upward  tilt,  the  upright  standards  are  still  further  shortened. 
For  carrying  the  copper  cables  a  much  lighter  structure  is  used, 
all  of  which  can  be  seen  from  the  illustrations.  Either  carbon  or 
graphite  electrodes  can  be  used  and'  changed  quickly;  either 
hand  or  automatic  electrode  control  is  furnished.  The  oVal 
shape  and  turtle-back  construction  of  the  roof  makes  a  strong 
construction,  standard  brick  being  used  throughout  for  the  roof 
construction,  excepting  a  few  special  electrode  bricks. 

The  electrical  connections  are  exceedingly  simple,  being 
merely  three  sets  of  cables  from  the  transformers  to  the  elec- 
trodes, and  no  complication  on  the  high-tension  side.  Elec- 
trically the  furnace  conditions  are  satisfactory  to  the  central 
station  managers,  the  power  factor  being  around  90%,  and 
the  phases  not  being  distorted  more  than  with  other  arc 
furnaces.  After  continued  operation  it  has  been  observed  that 
the  furnace  does  not  bulge  at  all,  this  being  another  indication 
of  the  even  heat  distribution  already  mentioned. 

The  furnace  is  equally  well  adapted  for  melting  down  miscel- 
laneous steel  scrap  for  castings  on  either  its  solid  acid  or 
basic  bottom,  selected  scrap  for  quality  and  tool  steels,  or  for 
melting  down  cast-iron  borings,  or  the  like,  for  use  with  malle- 
able iron,  or  for  melting  ferro-manganese. 

The  furnace  is  made  in  sizes  from  >^  ton  up  to  30,  and  for 
any  electrical  condition.  Regarding  installations  of  this  furnace, 
reference  is  had  to  the  statistics  on  another  page.  The  patents 
for  France,  Belgium,  Italy,  Switzerland,  and  Spain  have  been 
disposed  of  to  Le  Flaive  6s  Co.,  St.  Etienne,  France.  For  the 


GENERAL   REVIEW 


283 


284   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

United  States,  Canada,  and  elsewhere,  this  furnace  is  handled 
by  C.  H.  Vom  Baur,  New  York.1 

The  Ludlum  electric  furnace  has  recently  made  its  ap- 
pearance. It  has  a  solid  refractory  bottom,  uses  3-phase  cur- 
rent with  3  electrodes  in  one  line  with  a  charging  door  at  either 
end  of  its  major  axis,  and  the  spout  at  one  door.  It  uses  graphite 


FIG.  121  h. 

electrodes  only.  Its  efficiency  is  increased  due  to  the  particularly 
low  roof  (which,  however,  has  already  been  raised  by  means  of  a 
steel  filler  piece,  see  Fig.  121  h). 

The  roof  refractories  consequently  do  not  last  as  long  as 
with  the  arc  furnaces  of  a  similar  type,  having  a  corresponding 
higher  roof.  The  furnace  is  hexagonal  in  shape  as  seen  from  the 
picture,  and  gradually  slopes  to  an  oval  at  the  hearth. 

The  manufacturers  mention  the  following  details  in  design 
of  this  furnace  as  follows: 

The  design  and  shape  of  the  furnace  permit  the  supplying 

1  In  Scandinavia  and  Finland  this  furnace  is  handled  by  Henning  Broms, 
Ferdsgatan  6,  Stockholm. 


GENERAL    REVIEW  285 

of  energy  to  the  furnace  at  a  high  rate  within  the  critical  limits 
of  the  refractories,  resulting  in  quick  heats  and  a  low  power  con- 
sumption per  ton  of  metal,  besides  giving  a  thorough  refining 
by  reason  of  the  larger  area  of  contact  between  slag  and  the 
steel  compared  to  a  round  furnace  of  equal  capacity. 

The  arrangement  of  the  electrodes,  which  are  connected  to 
3 -phase  system,  results  in  producing  an  equal  amount  of  heat 
at  each  electrode;  the  greater  amount  of  heat  in  proportion  to 
the  mass  of  the  bath  at  the  ends  compensates  for  the  greater 
radiation  at  the  doors,  and  results  in  an  even  temperature 
at  the  side  walls,  makes  sintering  of  the  lining  easy,  reduces  the 
danger  of  the  breakage  of  electrodes  and  as  the  maximum  space 
for  operating  rabbles,  test  spoons,  etc.,  is  available  without 
coming  in  contact  with  the  electrodes. 

The  entire  bath  is  accessible  from  the  doors,  and  lining  can 
be  inspected  and  easily  repaired,  thus  simplifying  the  care  of 
the  bottom  and  increasing  its  life. 

The  hearth  meets  the  roof  with  hardly  more  intervening 
vertical  side  walls  than  shown  in  the  picture.  Standard  shaped 
brick  are  used  in  the  roof  and  hearth. 

The  arrangement  of  the  electrodes  and  shape  of  the  bottom 
result  in  the  formation  of  a  little  pool  which  extends  to  all 
three  electrodes,  at  the  time  they  have  cut  through  the  charge. 
This  metal  protects  the  bottom  refractories  from  the  arcs  and 
allows  melting  from  the  bottom  up  without  endangering  the 
lining.  The  furnace  may  be  provided  with  either  a  basic  or 
an  acid  lining.  This  furnace  is  handled  by  the  Ludlum  Electric 
Furnace  Corp.,  New  York. 

Other  proposals  consist  usually  of  combinations  that  in  most 
cases  would  bring  about  great  difficulties  in  operation,  and  which 
offer  no  advantages  over  the  original  furnaces.  Here  belong 
those  which  take  an  ordinary  metallurgical  furnace,  such  as  an 
open  hearth,  and  operate  it  at  certain  times  by  a  stoppage  of  the 
gas,  and  the  use  of  carbon  electrodes.  Also  a  combination  of 
converter  and  electric  furnace,  for  instance,  a  small  converter 
with  an  arc  furnace  built  in.  With  these  combinations  the 
conditions  of  operation  have  not  been  considered  carefully 
enough.  For  instance,  an  open-hearth  furnace  in  comparison 


286      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

with  an  electric  furnace  has  such  a  high  roof,  and  large  working 
surface  of  bath,  that  the  heat  losses  when  using  carbon  electrodes, 
even  if  only  for  the  desulphurizing  period,  would  bring  about 
much  too  high  costs.  In  these  cases  it  is  therefore  much  better 
to  transfer  the  charge  from  the  open-hearth  furnace,  or  the 
Bessemer,  to  a  special  electric  furnace  by  means  of  a  casting  ladle, 
and  to  stand  the  unavoidable  heat  losses.  In  this  way  cheaper 
and  better  results  will  be  obtained  than  with  any  of  the  pro- 
posals mentioned  above,  and  although  really  seriously  tried  out 
up  to  the  present  has  not  been  successful. 

As  a  conclusion  to  this  review,  which  is  believed  to  embrace 
the  most  valuable  proposals  in  the  different  spheres,  it  may  be 
established  that,  until  the  invention  of  further  types  of  con- 
struction, we  have  only  to  deal  with  those  described  in  detail  in 
the  special  chapters.  These  furnaces  still  show  many  weaknesses 
in  comparison  with  the  ideal  furnace,  yet  they  show  that  in  those 
with  the  greatest  simplicity  the  ideal  has  been  closely  approached. 


CHAPTER  XVI 

FINAL  CONSIDERATIONS 

THE  purely  technical  side  of  the  application  of  electric  fur- 
naces to  the  iron  and  steel  industry  has  been  considered  in  the 
foregoing  chapters,  so  that  now  something  may  be  said  with 
regard  to  the  economical  questions  of  electric  heating.* 

We  have  seen  already  in  Chapter  I  that  the  development  of 
electric  furnaces  is  closely  connected  with  that  of  electro-tech- 
nology. This  is  still  the  case  when  the  question  as  to  whether 
the  installation  of  an  electric  furnace  under  certain  conditions 
will  be  an  economic  success  or  not  is  under  discussion.  Then, 
indeed,  the  cost  of  the  electric  current,  which  is  the  heating 
agent  of  the  electric  furnace,  is  of  real  influence  for  the  success 
of  an  electric  steel  plant.  It  must  be  taken  into  consideration 
that  electricity,  in  by  far  the  most  cases,  is  much  more  expensive 
than  the  ordinary  methods  of  heating,  nevertheless  this  disad- 
vantage is  more  than  equalized  by  other  advantages. 

In  this  connection  we  may  quote  from  Borchers'  address 
before  the  Verein  Deutscher  Eisenhuttenleute,  in  1905.  "If  we 
reckon  the  kilogram  of  carbon  in  coke  at  a  high  price,  say  about 
0.7I4C.,  then  1000  kg.  calories  will  cost  o.o88c.  Very  cheap 
electric  power,  namely  at  $9.52  per  h.p.  year,  gives  1000  kg. 
calories  from  o.i67c.  to  o.2i4c.  according  to  the  number  of  work- 
ing days.  This  disadvantage  of  electric  heat  production  is  bal- 
anced by  this  condition;  that  the  material  to  be  heated,  which  in 
this  case  is  the  charge  itself,  accomplishes  partly  or  altogether  the 
transformation  of  the  electric  energy  into  heat.  In  a  certain 
way  it  forms,  of  itself,  the  source  of  heat,  while  in  all  combustion 
furnaces  the  heat  goes  first  to  a  mixture  of  gases,  and  from  this 
to  the  material  to  be  smelted." 

*  For  a  more  detailed  discussion  see  Part  II  under  "Costs  of  Operation." 

287 


288   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

In  the  above  example  the  price  of  power  taken  is  very  cheap, 
for  with  $9.52  per  h.p.  year,  and  assuming  300  working  days  in 
the  year,  the  kw.  hour  only  costs  o.iySc.  Such  a  low  figure 
is  only  to  be  reached  with  the  use  of  very  suitable  water-powers, 
while  it  is  unattainable  by  using  blast-furnace  gas,  provided  that 
the  blast-furnace  gas  is  reckoned  at  a  cost  corresponding  to  its 
heating  value.  If  this  is  done  then  it  will  usually  happen  that, 
even  with  the  use  of  large  gas-engines,  the  kw.  hour  cannot  be 
furnished  lower  than  0.357^  to  0.714^  Still  more  unfavorable 
are  the  results  if  steam  is  used,  although  here,  also,  progressive 
engineering  has  brought  about  a  constant  cheapening  in  the 
price  of  current.  For  instance,  in  well-conducted  central  stations, 
with  the  use  of  large  steam  turbines,  it  has  been  found  possible 
to  produce  the  kw.  hour  at  about  0.714^,  when  the  coal  does 
not  cost  more  than  o.4ic.  per  kw.  hour.  This  is,  of  course, 
provided  that  the  demand  for  power  is  very  uniform,  and  free 
from  variation,  for  otherwise  the  price  per  kw.  hour  is  increased 
considerably.  In  this  connection  von  Rizzo,  in  the  Electro- 
technische  Zeitschriit,  p.  596,  1910,  gives  a  figure  of  i-3ic., 
the  power  being  produced  by  steam,  and  being  used  for  operating 
a  railroad  with  a  very  variable  load. 

The  prices  given  have  reference,  almost  always,  to  large 
central  stations,  such  as  large  iron  and  steel  plants,  city  stations, 
etc.  With  smaller  producing  plants  the  price  of  current  naturally 
rises  considerably.  It  is  therefore  recommended  that  small 
plants  should  almost  always  be  connected  to  some  large  central 
station  for  their  electric  furnace  power,  if  the  opportunity  is 
there.  Such  stations  today  often  furnish  power  for  o.942c.  to 
i.428c.  per  kw.  hour,  which  is  a  price  that  cannot  be  realized 
in  small  power  stations,  except  with  high  pressure  internal 
combustion  oil  engines. 

We  see  then  that  the  source  of  power  used  for  the  production 
of  electricity  can  affect  the  price  of  current,  and  therefore  the 
production  costs  of  electric  steel.  Also  the  way  the  current  is 
used  plays  a  very  important  part,  and  this  depends  in  the  first 
instance  on  the  method  of  working.  The  following  table  shows 
how  this  method  of  working  influences  the  power  consumption: 


FINAL    CONSIDERATIONS  289 

It  requires  for  the  production  of: 

Pig  iron,  direct  from  ore 2,000  Kw.  Hrs. 

Steel,  direct  from  ore 3,000          " 

Steel  from  cold  pig  iron 1,500          " 

Steel  from  fluid  pig  iron 1,000-1,200         /' 

Steel  from  cold  pig  iron  and  cold  scrap 900-1,300          " 

Steel  from  molten  pig  iron  and  cold  scrap. .    600-1,000          " 

Steel  from  cold  scrap 600-900 

Refining  of  molten  low  carbon  steel  to  make 

special  quality  steel  (with  very  complete 

chemical     purification)      crucible      steel 

quality 200-300         " 

Refining  of  molten  low  carbon  steel  to  ordinary 

electric  steel  (electric  rails) 120         " 

Retaining  pig  iron  molten  for  foundry  purposes 

(heated  mixer) 50         " 

These  values  can  naturally  only  serve  as  rough  estimates, 
because  the  composition  of  the  charge  and  the  finished  material 
are  absolutely  necessary  for  more  exact  figures.  Further,  more  or 
less  power  will  be  used  according  to  the  efficiency  of  one  or  the 
other  furnace,  so  that  with  the  same  charge  and  finished  product 
different  power-consumption  figures  will  be  given  by  two  furnaces 
of  different  types. 

The  wide  limits  given  for  working  mixtures  of  pig  iron  and 
scrap  are  necessary  because  the  power  consumption  is  greatly 
dependent  on  the  percentage  of  pig  iron  and  of  scrap  used,  more 
being  necessary  with  an  increase  of  pig  iron.  Further  details 
on  these  points  are  given  in  the  second  part  of  the  book. 

From  what  has  been  said  it  is  apparent  that  the  price  of 
current  becomes  more  of  a  determining  factor  (for  the  efficiency 
or  non-efficiency  of  electric  furnace  operation),  according  to  how 
many  of  the  metallurgical  processes  necessary  for  changing  ore 
to  steel  are  carried  out  in  the  electric  furnace.  For  instance, 
when  fluid  metal  from  a  converter  or  open-hearth  furnace  is 
worked  the  cost  for  power,  with  an  average  unit  price  (o.476c. 
to  0.7I4C.  per  kw.  hour),  is  about  3%  of  the  production  cost; 
but  it  increases  to  12%  with  the  same  price  per  unit,  when  scrap 
is  worked. 

Finally  we  must  remember  that  all  of  the  furnaces  in  use 


290      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

today  have  certain  special  advantages.  Unfortunately  each 
type  of  furnace  has  also  certain  disadvantages.  These  disad- 
vantages are  so  closely  connected  with  the  methods  of  heating, 
that  they  must  be  allowed  for.  If  electric  steel  production  is 
entered  into  today  one  of  the  existing  furnaces  must  be  chosen, 
and  its  advantages  and  disadvantages  purchased  together.  It 
is  therefore  not  without  interest  to  see  how  widely  distributed 
the  various  types  have  become  up  to  date.  The  following 
statistical  tables  date  up  to  July,  1919. 

The  tables  show  that  the  more  important  furnace  types 
have  already  become  so  wide-spread  that  they  must  be  considered 
to  have  passed  the  experimental  stage.  At  the  same  time  the 
electric  furnace  has  shown  that  it  is  of  considerable  economic 
importance  because  it  has  enabled  the  production  of  the 
very  best  finished  steel  from  low  priced  material.  Until  now  the 
purest  and  therefore  the  dearest  raw  materials  were  necessary 
for  this  purpose.  The  tables  clearly  show  that  this  great  econo- 
mic advantage  of  the  electric  furnace  is  becoming  known  more 
and  more. 

When  we  realize  that  the  Stassano,  Heroult,  and  Kjellin 
furnaces  were  first  brought  out  in  1900,  and  the  Girod  and 
Rochling-Rodenhauser  in  1906  and  1907,  the  wide-spread  dis- 
tribution of  these  furnaces  takes  on  greater  importance.  How 
quickly  this  distribution  increases  is  also  shown  by  the  table,  for 
in  addition  to  895  furnaces  contracted,  all  but  80  are  in 
operation. 

It  may  be  concluded  by  pointing  out  that  the  electric  furnace 
is  already  firmly  established  in  the  iron  and  steel  industry,  that 
the  present  development  of  electric  furnace  plants  has  been 
very  rapid,  and  that  'an  important  future  is  assured. 


FINAL   CONSIDERATIONS 


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Part  Two 


A.  THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION, 
AND  THE  COSTS  OF  OPERATION 


THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION 
BY  DIPL.  ING.  W.  RODENHAUSER,  E.E. 

IT  has  already  been  pointed  out  several  times  that  a  great 
advantage  of  the  electric  furnace  over  other  metallurgical 
furnaces  is  that  it  enables  the  generation  of  desirable  high 
temperatures.  Generally  speaking  this  possibility  is  made  use 
of,  and  work  is  carried  out  at  higher  temperatures  than  in  gas 
fired  furnaces.  On  this  account,  therefore,  it  is  immediately 
apparent  that  the  materials  used  for  furnace  construction, 
especially  those  parts  in  contact  with  the  highly  heated  charge, 
have  to  meet  particularly  high  requirements.  Mistakes  in  the 
choice  of  these  materials  can  very  quickly  bring  about  trouble 
in  the  working  of  the  furnace  and,  under  certain  conditions,  can 
completely  stop  the  operation. 

During  the  discussion  of  the  different  furnaces  the  materials 
at  present  used  for  their  construction  were  mentioned,  but  it 
still  appears  advantageous  in  the  following  pages  to  treat  these 
materials  as  a  whole,  and  with  special  regard  to  the  conditions  of 
service. 

The  first  requirement  to  be  demanded  is  resistance  to  the 
high  temperatures  reached  in  the  furnace.  This  needs,  in  the 
first  place,  a  high  melting  point,  which  is  usually  measured  by 
means  of  Seger  cones.  These  are  named  after  their  inventor 
Seger.  They  are  small  three-cornered  pyramids  made  of  various 
mixtures  of  silicates,  and  are  about  2.36"  high.  The  softening 

292 


THE   MATERIALS  USED  IN  FURNACE  CONSTRUCTION        293 


point,  with  increasing  temperatures,  is  carefully  observed.  The 
following  table  gives  the  comparison  between  degrees  Centigrade 
and  Seger  cone  numbers. 


No. 

Temp. 

No. 

Temp. 

No. 

Temp. 

No. 

Temp. 

022 

600 

073 

960 

9 

1,280 

29 

1,650 

021 

650 

o6a 

980 

10 

1,300 

30 

1,670 

020 

670 

053 

I.OOO 

ii 

1,320 

31 

1,690 

OI9 

690 

o4a 

I.O2O 

12 

1,350 

32 

,710 

018 

710 

03a 

1,040 

13 

1,380 

33 

,730 

017 

730 

O2a 

1  ,060 

14 

1,410 

34 

,750 

016 

750 

Ola 

1,  080 

15 

1,435 

35 

,770 

oi  5a 

790 

la 

,100 

16 

1,460 

36 

,   ,790 

0143 

815 

2a 

,120 

17 

1,480   ; 

37 

,825 

oi3a 

835 

3a 

,140 

18 

1,500 

38 

,850 

oi2a 

855 

4a 

,160 

19 

1,520 

39 

,880 

ona 

880 

5a 

,180 

20 

1,530 

40 

1,920 

.  oioa 

900 

6a 

,200 

26 

1,580 

4i 

1,960 

oga 

920 

7 

,230 

27 

1,610 

42 

2,000 

o8a 

940 

8 

,250 

28 

1,630 

A  material  is  called  refractory  if  its  softening  point  lies  about 
No.  26,  and  very  refractory  if  the  latter  is  between  30  and  36. 

Without  going  further  into  the  properties  which  influence 
the  refractoriness  of  the  furnace  materials,  we  will  learn  the 
requirements  they  have  to  meet. 

The  first  consideration  is  that  in  electric  furnaces  the  materials 
are  exposed  not  only  to  high  temperatures,  but  also  to  chemical 
influences.  Naturally  the  results  of  these  influences  must  be 
felt  as  little  as  possible.  We  can  give  as  the  second  requirement 
great  resistance  to  chemical  influences.  Unfortunately  these 
harmful  influences  cannot  be  altogether  prevented,  and  it  is 
necessary  to  reduce  them  as  much  as  possible.  This  is  partially 
brought  about  by  having  the  greatest  possible  density  and 
mechanical  solidity  of  the  materials.  It  is  immediately  evident 
that  these  properties  are  of  important  influence  on  the  durability 
of  the  furnace  masonry  and  lining,  when  it  is  realized  that  porous 
material  offers  much  more  surface  for  attack  by  harmful  chemical 
influences  than  one  that  is  dense.  Further  great  density  is 


294    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

synonymous  with  good  mechanical  strength,  so  that  a  dense 
material  will  most  successfully  withstand  the  mechanical  in- 
fluences due  to  movements  of  the  electric  furnace. 

The  appearance  of  cracks  in  the  furnace  walls  lead  to  the 
same  bad  results  as  the  use  of  porous  material,  for  they  allow 
the  harmful  chemical  influences  to  penetrate  very  deep,  and 
offer  a  large  surface  for  attack.  This,  therefore,  brings  about 
the  requirements  of  the  ability  to  withstand  the  influence  of 
changes  of  temperature.  These  cracks  are  due  to  variations  in  the 
temperature,  which  bring  about  expansion  and  contraction  in 
the  materials  used. 

The  requirements  for  the  materials  for  furnace  construction 
are  therefore: 

1.  Ability  to  stand  high  temperatures. 

2.  Resistance  against  chemical  influences. 

3.  Great  density  and  mechanical  strength. 

4.  Permanence  of  form  under  changes  of  temperature. 

The  materials  to  be  considered  are  as  follows,  each  of  which 
will  be  taken  up  separately  in  the  light  of  the  above  requirements: 

1.  " Schamotte "  or  fire-clay  bricks. 

2.  Acid  or  silica  bricks. 

3.  Half  "Schamotte"  or  half-silica  bricks. 

4.  Carbon  bricks  and  carbon  mixtures  for  ramming  into  place. 

5.  Basic  bricks  and  basic  material  for  ramming  into  place. 

6.  Zirconia*  bricks.    7.   Mortar. 

"  Schamotte "  fire  bricks  are  made  from  burnt  fire-clay 
known  as  Schamotte  or  Chamotte,  to  which  unburnt  clay  is 
added  as  a  binding  material.  The  clay  shrinks  more  or  less 
during  the  burning.  The  Schamotte  must  therefore  be  burnt 
as  thoroughly  as  possible.  The  more  Schamotte  in  proportion 
to  clay  is  used  in  the  brick  mixture,  the  less  is  a  strong  shrinkage 
to  be  feared.  Moreover,  the  shrinkage  can  be  partially  neutral- 
ized by  adding  quartz  or  quartzite  which  expand  during  heating 
to  the  mixture. 

Under  all  conditions  the  shrinkage  of  the  "Schamotte" 
brick  is  to  be  most  carefully  kept  in  mind,  because,  for  example, 

*See  "The  Use  of  Zirconia  as  a  Refractory  Material,"  by  Audley:    British 
Ceramic  Society,  1918. 


THE    MATERIALS    USED    IN    FURNACE    CONSTRUCTION        295 

the  use  of  this  material  in  furnace  roofs  would  be  disastrous 
As  opposed  to  the  "Dinas"  silica  bricks,  which  will  shortly  be 
described,  these  fire-bricks  have  the  advantage  that  they  are  not 
so  sensitive  to  changes  of  temperature,  and  this  advantage  is 
more  marked  the  less  unburnt  clay  is  used  in  the  mixture. 

Their  chief  importance  in  electric  furnace  work  is  for  heat 
insulation  purposes,  and  they  are  used  in  this  way,  for  example, 
in  the  induction  furnaces.  For  furnace  roofs  they  are  only 
applicable  if  the  temperature  attained  is  not  very  high,  and 
therefore  at  the  most  can  be  used  only  for  induction  furnaces. 

Acid  or  silica  bricks  are  greatly  used  in  electric  furnaces  for 
roofs.  They  are  very  rich  in  silica,  and  are  made  from  quartzite 
with  95  to  99%  silica,  and  ought  to  have  at  least  95%  when 
finished.  They  are  known  to  the  trade  as  English  "Dinas"  or 
Lime  Dinas  bricks.  For  the  Lime  Dinas  bricks  an  addition  of 
i  to  2%  of  lime  is  used  as  a  binding  agent,  usually  in  the  form  of 
cream  of  lime.  If  clay  is  used  instead  of  lime  the  quality  is  not 
quite  so  good,  the  bricks  containing  80  to  90%  silica,  and  being 
known  as  Clay  Dinas  or  German  Dinas  bricks. 

As  has  been  mentioned,  these  bricks  expand  considerably 
with  increasing  temperature.  This  is  less  noticeable  in  bricks 
made  from  certain  quartzites,  but  is  unavoidable  even  with  the 
best  materials.  Their  greatest  use  is  for  the  roofs  of  furnaces 
with  high  roof  temperatures,  such  as  all  the  arc  furnaces  have, 
and  because  of  their  expansion  with  heat  a  very  flat  roof  can  be 
maintained.  Unfortunately  these  bricks  are  very  sensitive  to 
changes  of  temperature,  and  offer  only  small  resistance  to  the 
action  of  slags.  They  are  therefore  practically  restricted  to  roof 
and  side-wall  construction. 

The  half  Schamotte  or  half  silica  bricks  are  between  the 
two  kinds  of  brick  just  described.  They  consist  of  a  mixture  of 
quartz  and  burnt  clay,  and  have  properties  corresponding  to  an 
excess  of  one  or  the  other  constituent. 

Carbon  mixtures  for  ramming  into  place  are  not  used  in 
steel-refining  furnaces;  because  of  the  great  affinity  between 
iron  and  carbon  they  are  quickly  destroyed,  and  undesirable 
carbon  enters  the  metal.  On  the  other  hand  carbon  mixtures 
have  been  often  used  in  electric  shaft  furnace  experiments  in 


296     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

their  double  capacity  as  refractory  materials  and  conductors  of 
the  current.  In  addition  to  this  a  silicon-carbide  brick,  or 
so-called  "carborundum"  brick,  is  used  in  the  arches  over  the 
doors,  and  for  the  supports  for  these  doors  to  just  above  the 
slag  line,  with  good  results.  These  brick  are  very  expensive, 
costing  usually  15  to  20  times  as  much  as  silica  brick.  Silicon 
carbide  is  a  product  of  the  electric  furnace.  When  bricks  are 
made  of  it,  the  mass  is  crushed  to  small  particles,  mixed  with 
a  binder,  and  the  best  grades  again  burned  in  an  electric  heating 
furnace.  Zirconia  bricks  are  used  in  side  walls.  Their  higher 
initial  cost  than  magnesite  is  more  than  offset  by  their  high 
melting-point  resistance  to  slags,  low  thermal  conductivity,  low  ex- 
pansion value,  giving  increased  production,  and  higher  efficiency. 

Basic  bricks  and  materials,  however,  are  so  important  that 
they  are  used  largely  for  the  hearths  and  walls  of  electric  steel- 
making  furnaces.  They  include  chrome  iron  ore,  or  chromite, 
dolomite,  and  magnesite. 

Of  these  materials  chromite  is  not  used  in  Germany.  It 
has  the  disadvantage  that  if  it  comes  in  direct  contact  with  the 
metal  it  is  rapidly  destroyed,  and  influences  the  bath  in  an 
unwished-for  and  harmful  way. 

Dolomite  is  finding  increasingly  large  application.  It  is  a 
limestone  with  a  large  percentage  of  magnesia,  CaC03  MgC03 
and  is  found  in  large  amounts  in  Thiiringen  and  Lothringen, 
and  in  various  parts  of  the  United  States.  Its  greatest  use  in 
the  iron  and  steel  industry  is  as  a  lining  for  the  basic  Bessemer 
converter  for  which  it  is  prepared  in  so-called  dolomite  plants. 
The  method  of  preparation  may  be  briefly  described : 

The  raw  dolomite  is  either  broken  by  hand,  or  crushed,  to 
pieces  about  the  size  of  one's  fist.  These  pieces  are  then  burnt 
in  a  shaft  furnace  to  a  clinker.  The  amount  of  coke  necessary 
is  from  20%  to  30%  of  that  of  the  raw  stone.  After  burning,  the 
clinker  is  ground  in  a  suitable  mill,  the  largest  pieces  being  not 
more  than  10  mm.  (0.4")  diameter.  The  ground  dolomite  is 
then  mixed  with  about  7  to  10%  of  hot  dry  tar,  on  a  moderately 
heated  floor.  This  mixing  is  carried  out  either  by  hand  or  in 
a  chili  mill,  or  suitable  mixing  machine,  which  is  so  constructed 


THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION          207 

that  the  material  can  be  heated.  Careful  attention  must  be 
paid  to  the  preparation  of  the  tar  if  the  basic  dolomite-tar  mix- 
ture is  to  have  the  best  properties.  The  crude  tar  is  distilled  in 
special  apparatus  at  240-280°  C.,  and  is  freed  in  this  way  from 
the  ammonia  water  and  light  oils.  It  must  be  mentioned  that 
the  burnt  dolomite,  because  of  its  large  lime  contents,  readily 
absorbs  moisture  from  the  air  and  falls  to  powder.  It  should, 
therefore,  be  used  as  soon  after  its  preparation  as  possible,  and  is 
applicable  to  the  making  of  bricks,  or  for  ramming  into  place. 

Magnesite,  as  well  as  dolomite,  is  finding  an  increasingly 
large  use  for  those  parts  of  the  furnace  in  direct  contact  with  the 
charge,  and  indeed  for  all  those  parts  exposed  to  specially  high 
temperatures.  It  has  an  advantage  over  dolomite  in  that  it  is 
more  neutral  in  character.  When  mined  it  has  a  melting  point 
about  equal  to  Seger  cone,  No.  42.  As  it  shrinks  a  great  deal 
when  heated,  it  must,  before  using,  be  burnt  so  thoroughly  that 
it  is  sintered.  For  this  a  temperature  of  about  1700°  C.  is 
necessary,  and  the'Sp.  Gr.  rises  from  3.19  to  3.65.  If  the  magne- 
site  is  to  be  used  direct,  it  is  mixed  with  tar,  like  the  dolomite,  and 
rammed  into  place.  If,  however,  it  is  to  be  made  into  bricks,  no 
tar  is  used.  The  finely  powdered  magnesite  is  forced  into  shape 
by  the  use  of  very  high  hydraulic  pressure,  and  then  again  burnt. 

Apart  from  its  greater  neutrality  magnesite  has  the  further 
advantage  over  dolomite  that  it  is  not  so  sensitive  to  the  action 
of  moisture,  and  when  burnt  to  sinter  can  be  kept  in  storage 
without  fear  of  spoiling.  On  account  of  its  great  density,  how- 
ever, it  easily  cracks  when  subjected  to  changes  of  temperature, 
but  does  not  shrink  very  much  with  increasing  temperature,  and 
because  of  this  is  being  used  sometimes  for  furnace  roofs. 

When  building  electric  furnaces  a  suitable  mortar  must  be 
used.  Here  again  permanence  of  form  under  changes  of  tempera- 
ture is  of  the  first  importance,  and  the  mortar  must  be  carefully 
considered  in  this  respect.  Also  the  courses  should  be  laid  as 
close  as  possible,  so  that  even  with  expansion  of  the  mortar  the 
joints  may  remain  tight,  and  expose  very  small  surfaces  of  at- 
tack to  harmful  influences.  As  a  general  rule  it  may  be  said 
that  the  mortar  should  be  of  the  same  nature  as  the  rest  of  the 


298     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

construction,  using  basic  mortar  with  basic  materials,  and  acid 
with  acid.  Thus  with  dolomite  bricks  either  tar  alone  is  used, 
or  tar  mixed  with  dolomite  as  a  binding  material,  while  with 
magnesite  bricks  powdered  magnesite  is  used  mixed  either  with 
tar  or  a  little  hydrochloric  acid.  With  other  than  basic  brick- 
work a  certain  amount  of  quartz  or  white  silica  sand  is  usually 
mixed  with  the  mortar,  an  excess  of  clay  being  avoided,  and 
care  again  being  taken  to  have  tight  joints. 

Reconsidering  the  materials  of  construction,  we  see  that  none 
of  them  possesses  completely  the  qualities  that  have  been  men- 
tioned, so  that  they  must  be  carefully  chosen  and  used  with 
proper  regard  to  their  properties.  This  leads  us  to  a  point  that 
must  riot  be  left  without  attention.  It  is  that,  under  the  influ- 
ence of  other  materials  at  high  temperatures,  certain  refrac- 
tories quickly  break  down.  The  following  rule  must  be  strictly 
observed :  In  the  presence  of  basic  influences  use  basic  materials, 
and  with  acid  influences  use  acid  materials.  Therefore,  in  a 
furnace  in  which  the  basic  process  is  to  be  carried  out,  basic 
materials  must  be  used  completely  or  at  least  in  those  parts 
where  the  temperature  is  high  enough  for  one  material  to  act 
on  the  other.  On  the  other  hand,  in  the  Heroult  and  Girod 
furnaces  the  hearth  is  basic  but  the  roof  is  of  silica  bricks.  This 
is  only  possible  when  no  danger  of  fusion  is  to  be  feared  at  the 
junction  of  the  two  materials.  It  should  be  remembered  that 
quartz  and  clay,  or  mixtures  of  the  two,  so  greatly  lower  the 
melting  points  of  dolomite  or  magnesite  as  to  bring  them  from 
Seger  cone  17  to  n,  which  would  naturally  lead  to  the  rapid 
destruction  of  any  electric  furnace  if  it  took  place. 

The  extremely  harmful  occurrences  mentioned  here  must  be 
prevented,  either  by  the  use  of  basic  material  exclusively,  or 
else  the  contact  between  the  acid  roof  and  basic  hearth  must 
be  removed  from  the  influence  of  harmful  temperatures. 

It  may  be  mentioned  here  that  the  lowering  of  the  fusion 
point  of  a  refractory  material  is  often  brought  about  purposely, 
however,  only  to  a  certain  degree.  For  instance,  in  making  a 
hearth  of  magnesite,  slag,  clay,  or  similar  material  is  often 
added  as  a  flux,  to  bring  about  a  more  ready  sintering  of  the 


THE    MATERIALS    USED    IN   FURNACE    CONSTRUCTION        299 

mass.  In  this  way  the  hearth  is  made  denser,  and  offers  greater 
resistance  to  the  influence  of  the  metal  and  slags.  Naturally 
only  the  smallest  amount  of  flux  necessary  must  be  used  in  order 
not  to  reduce  the  melting  point  too  much. 

In  the  design  of  electric  furnaces  the  properties  of  the  mate- 
rials to  be  employed  should  be  carefully  kept  in  mind.  In  the 
first  place  the  side  walls  ought  to  be  of  such  a  shape  that,  after 
a  charge  or  a  short  run,  repairing  can  be  carried  out.  This  is 
necessary  because  of  the  unavoidable  action  of  the  slag  on  the 
lining.  This  is  completely  possible  at  present  only  in  that  fur- 
nace which  is  patterned  after  the  open  hearth,  except  for  the 
rectangular  shape.  All  furnaces  allow  a  certain  amount  of  re- 
lining,  with  even  the  vertical  or  almost  vertical  walls  it  is 
easily  possible  to  keep  these  longer  than  3  to  4  weeks.  After 
this  time  a  new  one  is  necessary,  equally  with  the  Heroult, 
Girod,  or  Rochling-Rodenhauser.  Notwithstanding  this,  the 
previous  discussions  on  costs  of  operation  have  shown  that 
the  lining  costs  of  the  Heroult  and  Rochling-Rodenhauser  are 
about  the  same.  This  is  because  quicker  roof  destruction  in 
the  arc  is  counterbalanced  by  the  bottom  renewal  of  the  induc- 
tion furnace. 

It  is  because  of  these  considerations  that  the  Stassano  and 
Girod  furnaces  do  not  have  such  good  lining  costs  as  the  Heroult 
and  Rochling-Rodenhauser.  In  case  bricks  are  not  used  the 
new  hearth  is  sometimes  made  up  of  hot  magnesite  or  dolomite 
mixture  rammed  into  place.  If  this  work  has  been  carried  out 
by  hand  it  can  be  more  profitably  done  by  means  of  compressed 
air  hammers  which  are  sold  by  all  the  firms  making  compressed- 
air  tools.  Air  at  a  pressure  of  about  six  atmospheres  is  used. 
These  tools  bring  about  a  great  saving  in  labor,  and  have  the 
advantage  that  they  also  give  a  much  denser  and  more  solid 
hearth  than  hand  ramming.  Naturally  if  such  a  lining  is  heated, 
which  corresponds  somewhat  to  the  burning  of  refractory  bricks, 
an  expansion  takes  place.  This  will  certainly  give  rise  to  cracks 
unless  a  certain  freedom  of  movement  is  allowed  for.  This  is  well 
provided  for  by  leaving  a  space  between  the  hearth  and  the  in- 
sulating cover,  which  may  be  filled  with  loose  granulated  material. 


300     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

In  all  arc  furnaces  the  roof  is  made  removable,  for  repairs 
are  not  possible  during  the  operation.  In  this  way  a  new  roof 
can  easily  and  quickly  be  put  into  place.  As  the  bricks  used 
for  the  roofs  are  sensitive  to  changes  of  temperature,  it  is  evi- 
dent that  there  will  be  more  danger  the  more  water-cooled 
openings  there  are  through  which  to  pass  electrodes.  A  very 
superior  basic  bottom  material,  consisting  of  about  87%  CaO 
and  13%  FeO  sintered  together,  has  been  brought  out  by  the 
Coplay  Cement  Co.,  Coplay,  Pa.,  U.  S.  A.  This  lends  itself 
even  better  than  magnesite  for  patching  basic  bottoms  need- 
ing no  flux  to  make  it  set.  Bottoms  are  also  burned  in  with 
the  arc  only,  layer  by  layer,  without  using  flux,  which  last  a 
year.  This  material  can  be  exposed  to  the  weather  without  be- 
coming hydroscopic.  It  sells  at  a  reasonable  price  per  ton. 

THE  COSTS  OF  OPERATION 

The  question  of  the  operating  costs  of  electric-steel  and 
pig-iron  processes  is  undoubtedly  the  most  important  one  after 
that  of  the  quality  of  the  product.  These  two  questions  there- 
fore will  determine  which  types  of  furnace  will  advance  in  the 
future,  and  which  will  recede.  With  regard  to  the  quality  it  is 
generally  acknowledged  that  all  the  accepted  types  of  electric 
furnaces,  those  considered  in  detail  in  the  chapters  of  the  first 
part  of  the  book,  will  produce  steel  that  will  answer  all  require- 
ments. However,  the  possibility  is  often  mentioned  of  an  un- 
favorable influence  on  the  quality  of  the  steel  of  the  unneces- 
sarily high  temperatures  of  the  arc  furnaces.  This  possibility  is 
brought  up  again  and  again,  and  was  recently  spoken  of  by 
Henry  M.  Howe,  Professor  of  Metallurgy  in  Columbia  Uni- 
versity (E.  &  M.  /.,  Aug.,  1909). 

During  the  past  ten  years  of  experience,  1900-1919,  the  high 
heat  of  the  arc  has  had  no  deleterious  effects  on  the  steel  which 
can  be  traced  at  this  time.  Howe  again  says,  1918,  of  all  elec- 
tric steels,  "At  any  rate,  it  grows  very  much  easier  for  us  to 
believe  and  to  accept  the  evidence  of  experience,  that  electric 
steel  is  better  than  open-hearth  steel,  from  the  fact  that  the 
electric  furnace  reproduces  very  closely  the  conditions  of  the 


THE    MATERIALS    USED    IN   FURNACE    CONSTRUCTION       301 

crucible,  particularly  in  that  it  has  very  much  closer  control 
over  conditions.  You  can  get  in  the  electric  process  much  closer 
controls  over  the  conditions  than  you  can  get  in  the  open  hearth 
and  very  much  closer  than  in  the  Bessemer."  Dr.  Jos.  W. 
Richards,  disagreeing  with  Howe  on  the  crucible  vs.  the  electric 
furnace,  says,  "You  cannot  get  in  the  crucible  such  slag  as  you 
wish,  you  can  get  only  an  acid  slag,  and  you  cannot  make  a  re- 
fining slag,  whereas  in  the  electric  basic,  with  far  inferior  material, 
you  can  make  a  basic  slag  produce  steel  substantially  equal  in 
quality  to  crucible  which  is  made  from  much  better  material." 

There  remains,  therefore,  only  the  question  of  the  operating 
costs  to  determine  which  type  of  furnace  to  adopt  and  the  econ- 
omy of  electric  steel  production.  Calculations  of  the  operating 
costs  of  the  different  types  of  furnaces  have  been  published  many 
times,  so  that  it  would  appear  very  simple  to  compare  them 
one  with  the  other.  This  would  immediately  show  which  one 
would  allow  the  cheapest  production  of  steel,  and  the  difficult 
question  of  the  choice  of  the  most  suitable  and  economical  type 
of  furnace  would  be  solved  at  one  blow.  Unfortunately  this 
method  is  altogether  incapable  of  giving  a  view  corresponding  to 
the  real  conditions.  The  figures  that  one  usually  finds  published 
are  often  misleading.  However,  some  of  them  should  be  con- 
sidered later,  for  with  proper  care  they  will  give  much  inter- 
esting information. 

First  we  will  see  which  factors  are  of  importance  in  influ- 
encing the  operating  costs.  They  are  briefly:  i.  The  mate- 
rials charged.  2.  The  loss  during  the  operation.  3.  The  con- 
sumption and  price  of  the  current.  4.  The  fluxes.  5.  The  labor 
costs.  6.  The  costs  of  linings  and  repairs.  7.  Amortization. 
8.  Costs  of  electrodes.  9.  Auxiliary  appliances.  10.  Tools. 

In  regard  first  of  all  to  the  material  charged,  it  can  be  of 
metal  below  the  average  in  quality,  and  therefore  cheaper,  for 
all  electric  furnaces  which  are  suitable  for  refining.  This  is  be- 
cause these  furnaces  allow  a  very  complete  removal  of  all  harmful 
impurities.  The  induction  furnaces  with  ring-shaped  hearths, 
such  as  the  Kjellin  furnace,  do  not  allow  thorough  refining  to 
be  carried  out,  as  has  been  pointed  out  in  the  previous  chapters. 


302      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

For  these  furnaces,  therefore,  especially  pure  and  correspondingly 
dearer  raw  materials  must  be  chosen,  similar  to  those  now  used 
in  the  crucible  process.  This  includes  the  high-priced  Swedish 
irons,  as  well  as  the  purest  refined  metal,  usually  made  from 
Styrian  charcoal  pig  iron;  also  fluid  metal  already  refined  in 
the  open-hearth  furnace,  which  can  be  "killed"  in  the  electric 
furnace,  in  exactly  the  same  way  as  in  the  crucible.  Such  a 
furnace  is  therefore  at  a  decided  disadvantage  with  regard  to 
the  metal  charged  compared  with  other  furnaces,  notwithstanding 
that  a  considerably  lower  power  consumption  is  naturally  re- 
quired for  the  further  working  up  of  pure  raw  material  compared 
with  material  that  must  be  first  refined  in  an  electric  furnace  of 
another  construction. 

For  these  electric  refining  furnaces,  the  cost  of  the  charge 
can  be  taken  as  equally  high  when  comparing  the  operating 
costs.  When  comparing  the  costs  of  the  open-hearth  and  basic 
electric  furnace  it  must  not  be  left  out  of  consideration  that 
the  latter  has  the  advantage  that  it  allows  the  use  of  more  impure 
and  therefore  cheaper  raw  materials,  at  the  same  time  permitting 
the  production  of  the  highest  quality  steels. 

It  appears  unnecessary  to  give  here  any  figures  on  the  price 
of  scrap,  for  as  already  mentioned  this  price  is  strongly  depend- 
ent on  local  conditions.  This  also  applies  to  fluid  charges  from 
either  the  blast  furnace,  cupola,  open-hearth  furnace,  or  converter. 

THE  LOSS  DURING  THE  OPERATION 

This  means  the  material  lost  during  the  treatment  of  the 
molten  metal  in  the  electric  furnace.  Compared  with  other 
furnaces  it  is  very  small.  When  using  the  purely  induction 
furnace  with  ring-shaped  hearth,  in  which  the  purest  material 
must  be  used,  the  loss  is  not  considered  at  all;  it  can  be  put  down 
as  zero.  On  the  other  hand,  when  carrying  out  refining  in  the 
electric  furnace,  a  certain  loss  is  unavoidable.  Altogether  apart 
from  the  slagging  of  the  impurities,  small  amounts  of  the  liquid 
metal  are  torn  away  when  the  slag  is  removed.  This  loss  is 
therefore  the  greater  the  more  impurities  are  present  in  the 


THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION          303 

charge  which  necessitates  a  more  frequent  making  and  removal 
of  slags.  One  will  scarcely  make  a  mistake  in  taking  this  loss, 
depending  on  the  charge,  as  about  the  same  in  all  electric  refining 
furnaces.  It  should  be  figured  on  the  average  as  4  to  6  per 
cent,  with  a  solid  charge,  and  2  to  3  per  cent,  with  a  liquid 
charge.* 

In  this  connection  it  must  be  remembered  that  very  light 
thin  scrap  can  be  used  in  the  electric  furnace  such  as  waste  wire, 
turnings,  etc.,  without  the  loss  being  higher  than  the  figures 
given  above.  This  is  because  the  strongly  oxidizing  action  of 
the  hot  gases  of  the  open  hearth  is  not  present  in  the  electric 
furnace.  For  comparison  it  may  be  mentioned  that  the  loss  in 
the  open-hearth  scrap  process  ordinarily  amounts  to  4  to  8  per 
cent.,  and  is  considerably  higher  if  much  of  the  light  scrap, 
mentioned  above,  is  used. 

If  a  pig-iron  process  is  carried  out  in  the  electric  furnace, 
which  can  offer  an  economic  advantage  under  very  favorable 
prices  for  current,  then  more  iron  is  reduced  from  the  ore  than  is 
the  case  in  the  open  hearth,  so  that  the  yield  is  easily  greater  in 
amount  than  that  charged.  In  this  respect  the  electric  furnace 
works  more  cheaply  than  the  open  hearth,  and  further  allows  the 
production  of  a  higher  quality  of  steel  than  can  be  produced 
in  the  open  hearth.  This  is  shown  very  plainly  in  that  steel  is 
often  taken  from  the  open  hearth  to  the  electric  furnace  to  be 
refined,  or  to  be  alloyed,  etc.  • 

In  view  of  these  advantages,  why  is  not.  the  electric  furnace 
used  more  often  for  melting,  in  place  of  the  open  hearth?  The 
answer  is  found  immediately  if  we  consider  the  cost  of  heating, 
on  the  one  hand  in  the  open-hearth  or  crucible  furnace,  on  the 
other  hand  in  the  electric  furnace.  The  fuel  consumption  in  the 
open  hearth,  working  the  scrap  process  and  using  bituminous 
coal,  amounts  to  22%  to  32%  of  the  output.  If  we  take  the 
highest  value,  and  remember  that  the  electric  furnace  in  the 
sizes  used  up  to  now  can  only  be  compared  with  small  open- 

*  Borchers  gives  the  loss  as  10  to  II  per  cent,  in  a  Girod  furnace  with  a 
cold  charge. 


304     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


hearth  furnaces,  we  find  that  320  kg.  (705.5  Ib.)  of  coal  would  be 
used  per  metric  ton  of  open-hearth  steel.  In  the  electric  furnace 
700  to  800  kw.  hours  would  be  necessary  to  melt  the  scrap  used 
in  the  open  hearth,  and  to  refine  it  to  the  same  grade  as  ordinary 
open-hearth  steel,  provided  that  the  furnace  was  of  5  to  8  tons 
capacity.  If  the  coal  cost  $3.57  per  ton,  then  the  heating  cost 
alone  of  the  open  hearth  would  be  $1.12  per  metric  ton.  In 
order  that  the  heating  cost  in  the  electric  furnace  should  not 
exceed  that  of  the  open  hearth,  the  kw.  hour,  with  the  above 
assumptions,  should  cost  0.150. 

If  the  kw.  hour  prices  are  calculated,  which  are  allowable 
with  different  prices  of  coal  and  coal  consumption,  so  that  the 
heating  costs  in  the  electric  furnace  do  not  exceed  those  in  the 
open  hearth,  then  the  following  table  is  obtained: 


Coal 

Used  per 
Metric 

Allowable  Price  per  Kw.  Hr.  in  Cents  with  Coal  at  the  Following 
Price  per  Metric  Ton  (2,204  Lbs.  ): 

If  there 
is  Used 
per 

Ton  of 

Metric 

Open- 

Ton  of 

Hearth 

$2.85 

13-33 

$3-80 

$4.28 

$4-76 

$5-23 

*5.7i 

Electric 

Steel 

Steel 

22 

.0833 

.097 

.III 

.126 

.140 

•154 

.  i66c. 

24 

.090 

.107 

.  121 

.138 

.152 

.166 

.183 

26 

.  IOO 

.116 

.130 

•147 

.164 

.180 

.197 

750 

28 

.107 

.123 

.140 

•159 

.178 

•195 

.214 

kw.hrs. 

30 

.114 

•133 

.152 

.171 

.190 

.209 

.228 

32 

.121 

.142 

.161 

.I83 

.202 

.223 

.238 

22 

.078 

.090 

.104 

.116 

.130 

.142 

.1570. 

24 

.085 

.100 

.114 

.128 

.142 

•157 

.171 

800 

26 

.092 

.107 

.    .123 

.138 

•154 

.I69 

-185 

kw.hrs. 

28 

.100 

.116 

•133 

.150 

.166 

.I83 

.200 

30 

.107 

.123 

.142 

•159 

.178 

•195 

.214 

32 

.114 

.133 

.152 

.171 

.190 

.209 

.228 

22 

•  073 

.085 

.097 

.109 

.123 

•135 

•  i47c. 

24 

.080 

.092 

.107 

.  121 

•133 

•H7 

.161 

850 

26 

.086 

.  102 

.116 

.130 

•145 

•159 

•173 

kw.hrs. 

28 

.092 

.109 

.126 

.140 

•157 

.171 

.188 

30 

.  IOO 

.116 

•133 

.150 

.166 

.183 

.202 

32 

.107 

.123 

.142 

.161 

.178 

.197 

.214 

This  table  clearly  shows  how  very  much  cheaper  the  heating 


THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION  305 

costs  are  in  the  open-hearth  than  in  the  electric  furnace.  With 
the  most  unfavorable  coal  consumption  (32%),  and  very  high  cost 
of- coal  ($5.71  per  metric  ton),  the  kw.  hour  ought  not  to  cost 
more  than  o.238c.  If  we  calculate  the  kw.  year  as  containing 
300  working  days,  then  the  kw.  year  ought  not  to  cost  more 
than  $17.14,  or  the  e.h.p.  year  must  not  cost  more  than  $12.62. 
It  is  evident  that  these  prices  for  power  can  only  be  reached 
with  the  most  favorable  conditions,  for  example  through  the 
use  of  water-power.  It  is  therefore  also  clear  that  the  electric 
furnace  can  only  be  used  for  the  melting  of  scrap,  and  the  pro- 
duction of  steel,  similar  in  quality  to  ordinary  open  hearth,  in 
such  places  where  the  cheapest  natural  power  is  ready  for  use,  or 
else  where  small  amounts  of  steel  are  to  be  made  for  which  the 
open-hearth  process  is  unsuitable.  In  all  other  cases  it  is  almost 
always  preferable  to  leave  only  the  final  work  to  the  electric 
furnace.  In  this  way  at  only  a  small  increase  in  cost  an  improved 
quality  is  reached,  compared  with  open  hearth  which  is  greatly 
in  favor  of  the  electric  furnace. 

The  smaller  crop  of  electric  steel  ingots,  and  when  the  latter 
are  rolled  into  sheets  for  galvanizing,  where  the  so-called 
"spangle"  is  larger  and  better  looking,  and  takes  less  spelter, 
compared  to  open-hearth  sheets,  are  all  offsets  which  must 
be  taken  into  consideration. 

It  has  been  mentioned  already  that  the  electric  furnace  can 
replace  the  crucible.  If  we  therefore  now  consider  the  heating 
costs  of  the  electric  furnace  on  the  one  hand  (using  this  method 
of  working),  and  the  crucible  on  the  other,  we  obtain  the  follow- 
ing: The  fuel  consumption  with  crucible  melting  in  coke 
furnaces  not  using  the  waste  gases  amounts  to  about  150  to 
200  per  cent,  of  coke,  and  with  the  use  of  regenerative  gas 
furnaces,  175  to  200  per  cent.  coal. 

If  we  take  it,  first,  that  the  same  pure  charge  is  to  be  used 
in  the  electric  furnace  as  in  the  crucible,  then  the  melting  capacity 
alone  of  the  electric  furnace  comes  into  consideration.  For  this 
the  power  consumption  is  600  to  750  kw.  hrs.  per  metric  ton  of 
finished  steel  depending  on  the  size  of  the  furnace  used.  For 
instance,  the  firm  of  Krupp  has  brought  the  power  consumption 


306    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


down  to  617  kw.  hrs.  per  metric  ton  in  their  8-ton,  ring-shaped 
induction  furnaces,  of  the  Kjellin  and  Frick  types.  Also,  calcu- 
lating on  the  melting  alone,  the  power  consumption  in  an  8-ton 
Rochling-Rodenhauser  furnace  is  only  580  kw.  hrs.  per  ton. 

Taking  the  figures  given  above  as  a  basis,  the  table  on  the 
following  page  clearly  shows  how  high  the  cost  per  kw.  hr. 
may  be,  in  order  that  electric  heating  may  not  be  dearer  than 
that  in  the  crucible  furnaces  with  the  given  unit  prices  for  coal 
and  coke. 

The  table  shows  how  the  unit  price  for  power  can  increase 
very  considerably  before  the  heating  cost  in  the  electric  furnace 


Coal 

Used  per 
Metric 

Allowable  Price  per  kw.  hr.  in  Cents  with  the  Following  Coal 
or  Coke  Prices  (per  Metric  Ton): 

If  there 
is  Used 

Mrtric 

Crucible 

Ton  of 
Electric 

Per  cent. 

$2.38 

$2.85 

$3-33 

$3.80 

$4.28 

$4.76 

$5-23 

$5.71 

Steel 
kw.  hrs. 

150 

•595 

.714 

.833 

•952 

I.07I 

1.190 

1.309 

1.428 

) 

175 

•695 

•833 

..971 

I.  in 

1.250 

1.388 

1.528 

1.666 

}•      600 

200 

•795 

•952 

I.  Ill 

1.269 

1.428 

1.588 

1-745 

1.904- 

) 

150 

•547 

•659 

.769 

.881 

.988 

I.IOO 

1.209 

I.3I9 

\ 

175 

•643 

.769 

.897 

1.028 

1.115 

1.281 

1.409 

1.540 

r   650 

2OO 

•733 

.881 

1.028 

1.171 

.1.316 

1.464 

1.614 

1.762 

) 

150 

.512 

.6€2 

.714 

.816 

.919 

1.  02  1 

1.123 

1.224 

j 

175 

•595 

.714 

•833 

•952 

1.071 

1.190 

1.309 

1.428 

>•    700 

200 

.681 

.8l6 

•952 

1.088 

1.226 

1.362 

1.500 

1-633 

) 

150 

.476 

•571 

.666 

.762 

•857 

•952 

1.047 

I-I43 

\ 

175 

•557 

:666 

•778 

.890 

1.  000 

1.  112 

I.22I 

1-333 

[   750 

200 

•635 

.762 

.890 

1.016 

1-143 

1.269 

1-397 

1.524 

> 

will  exceed  that  of  the  ordinary  crucible  furnaces.  We  had 
assumed  previously  that  only  pure  raw  materials  were  used. 
In  this  way,  however,  only  a  part  of  the  advantage  of  the  electric 
furnace  is  utilized  since  the  remarkable  properties  that  it  shows 
as  a  refining  furnace  remain  unemployed.  We  should  obtain, 
therefore,  a  still  more  favorable  idea  of  the  electric  furnace  if 
we  used  less  pure  and,  therefore,  cheaper  raw  material  in  the 
charge.  Although  from  150  to  250  kw.  hrs.  more  would  be 


THE    MATERIALS    USED    IN    FURNACE    CONSTRUCTION        307 

required,  depending  upon  the  degree  of  purification,  this  increase 
would  scarcely  outweigh  the  savings  brought  about  by  the  use 
of  a  cheaper  charge. 

It  must  be  further  considered  that  much  more  labor  is  re- 
quired to  operate  the  crucible  furnaces  than  an  electric  furnace, 
which  can  replace  many  crucibles  because  of  its  capacity.  This 
latter  property  brings  about  a  further  advantage,  namely,  a 
complete  uniformity  of  the  whole  cast,  while  the  material  from 
different  crucibles  shows  certain  variations.  It  should  also  be 
mentioned  that  the  cost  of  crucibles  is  higher  than  that  of  the 
upkeep  of  an  electric  furnace.  Finally,  when  one  considers 
that  the  steel  from  the  electric  furnace  is  of  fully  equal  value 
to  Uiat  from  the  crucible,  then  the  displacing  of  the  crucible 
by  the  electric  furnace  appears  inevitable.  This  is  shown  by 
the  growth  that  the  electric-furnace  industry  has  had  even  up 
to  now.  The  following  figures  in  metric  tons  are  taken  from 
the  steel  production  of  Austria-Hungary: 


Year                                         Crucible  Steel 


Electric  Steel 

1907 
1908 

23.215 
19,659 

4.333 

1909 

16,083 

9,048 

1910 

17,586 

20,028 

1911 

17,467 

22,867 

The  following  table  in  metric  tons  shows  the  steady  progress 
which  electric  steel  has  made  in  the  leading  steel  producing 
countries  of  the  world: 


1918                  1917 

1916 

1915 

1914 

United  States  
Germany  

870.000$ 
221,824 
147,925 
50,000! 

I2O,OOOt 

11,000 

304.542 
219,700 
120,600 
48.000! 
39,069 

10,664 

169,918 
190,036 
49,256 
47,247 
43.790 

6,648 

69.412 
1  29,000 
22,000 
23,895 
61 

24,009 
89.336 

"f" 

..... 

Austria,  Hungary,  Bohemia. 
Canada  
France 

Sweden  
• 
Totals  

i,420,749j 

742,575* 

506,895 

244,368 

1913 

1912 

1911 

1910 

1909 

1008 

United  States  
Germany  
Great  Britain  
Austria,  Hun.,  Boh.. 
Canada  
France  
Sweden  

30,180 
101,755 

26,837 

18,000 
t 

18,309 

74,177 
Vi'.SSO 
15.992 

29.105 
60,654 

aV.867 

'13,850 

52,141 
26,200 

20,028 
13,445 

13.762 
17,700 

9.048 
50 
6,456 
t 

55 
19.536 

4.333 
93 
3f4 

Totals  

176,772 

129,964 

126.476* 

*  Includes  Sweden. 


t  Data  not  available. 


t  Estimated. 


308      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

We  have  previously  shown  that,  in  regard  to  heating  costs, 
the  electric  furnace  is  more  economical  in  almost  all  cases  than 
the  crucible  furnace,  but  that  on  the  other  hand  it  usually  is 
less  economical  than  the  open  hearth.  This  naturally  brings 
it  about  that  as  much  as  possible  of  the  melting  and  refining 
should  be  done  in  the  more  cheaply  operated  open  hearth;  or, 
in  the  case  of  the  refining  of  basic  Bessemer  metal,  in  the  con- 
verter. This  leaves  only  refining  and  desulphurization  for  the 
electric  furnace,  for  both  of  which  purposes  it  is  particularly 
suitable,  because  of  the  easy  regulation  of  the  temperature,  and 
the  removal  of  the  harmful  influences  which  are  unavoidable 
with  any  other  method  of  heating. 

It  is,  therefore,  to  be  expected  that  the  electric  furnace 
will  not  only  displace  crucible  plants,  but  will  be  introduced 
more  and  more  in  connection  with  open-hearth  and  Bessemer 
plants. 

The  power  consumption  necessary  for  the  work  of  refining 
naturally  depends  greatly  on  the  final  product  desired,  but  it  is 
also  dependent  upon  the  degree  of  purity  the  material  has,  when 
charged  into  the  electric  furnace.  Furthermore,  the  size  of  the 
furnace,  as  well  as  the  efficiency  of  the  particular  type  of  furnace 
chosen,  has  an  influence  which  must  not  be  neglected.  In  re- 
gard to  these  latter  influences,  the  discussion  in  the  first  part 
of  the  book  must  be  consulted. 

The  only  points  remaining  to  be  considered  are  those  of  the 
material  charged,  and  the  final  product  required. 

It  is  known  that  in  melting  in  any  furnace  a  higher  effi- 
ciency is  obtained  the  quicker  the  melting  proceeds,  that  is, 
the  greater  the  amount  of  energy  supplied,  the  higher  the  effi- 
ciency. With  an  important  lessening  of  the  time  necessary  for 
melting,  there  is  a  corresponding  lowering  in  the  amount  of  neat 
lost  by  radiation,  etc.  It  is  also  well  known  that,  after  the 
melting  stage  is  once  over,  the  following  refining  period  cannot 
be  lowered  at  will  by  increasing  the  amount  of  energy  introduced, 
but  that  this  refining  work  requires  a  certain  time.  As  already 
mentioned  several  times,  the  slag  must  be  changed  more  fre- 
quently, depending  on  the  impurity  of  the  charge  and  the  required 


THE  MATERIALS  USED  IN  FURNACE  CONSTRUCTION          300 

purity  of  the  final  steel.  The  curve  given  in  Fig.  60  (see  Part  I, 
page  140),  which  shows  the  power  consumption  depending  upon 
the  size  of  the  furnace  with  different  slag  changes,  gives  a 
fitting  idea  of  the  influence  of  the  impurities  in  the  charge 
on  the  power  consumption.  The  figures  given  should  there- 
fore be  considered  as  approximate.  To  give  more  exact  values 
is  apparently  only  possible  with  a  thoroughly  fixed  type  of 
furnace,  of  a  fixed  size,  and  with  an  exactly  established  charge 
and  final  material. 

For  example,  basic  Bessemer  metal  with  about  0.08%  P 
and  0.08%  S,  requires  an  average  of  250  kw.  hrs.  per  metric 
ton  for  refining,  in  an  8-ton  Ro'chling-Rodenhauser  furnace, 
when  the  final  material  required  is  of  crucible  steel  quality 
with  a  definite  carbon  content.  With  the  production  of  the 
highest  value  alloy  steels  the  power  consumption  under 
almost  the  same  conditions  increases  to  280  and  even  300 
kw.  hrs.  per  metric  ton.  On  the  other  hand,  when  making 
structural  steels  it  falls  to  200  kw.  hrs.  or  less.  The  power 
consumption  is  therefore  the  smallest  when  only  a  limited 
allowing  or  degasification  must  be  carried  out,  and  not  a  thor- 
ough refining  of  the  metal.  It  then  falls  even  to  100  kw.  hrs. 
and  less  per  ton. 

It  should  be  remembered  that  very  impure  metal  was  taken 
for  the  charge,  basic  Bessemer,  and  if  metal  was  taken  from  the 
open  hearth  for  example,  with  0.03%  P  and  0.05%  S,  then 
under  the  same  conditions  there  would  be  a  certain  lowering 
of  at  least  50  kw.  hrs.  per  metric  ton  when  making  high  quality 
steels. 

The  considerations  given  above  serve  to  show  that  the 
power  consumption  figures  given  in  technical  papers  should 
be  carefully  investigated  to  see  what  conditions  they  refer  to, 
for  such  figures  only  lead  to  grave  mistakes  in  many  cases. 

As  the  electric  pig-iron  furnace  is  beginning  to  be  of  im- 
portance, as  shown  by  the  action  of  the  Jernkontoret  in  Sweden, 
who  have  built  a  furnace  for  a  daily  output  of  20  tons1  with  an 
energy  consumption  of  2,500  to  3,000  h.p.,  a  comparison  is  given 

1  In  1919  —  Average  size  is  45  tons. 


310    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

below  between  the  ordinary  blast  and  electric  shaft  furnace. 
The  following  table,  due  to  Catani,  is  taken  from  Neumann's 
paper  in  Stahl  und  Eisen,  1909,  p.  276  ff.  It  shows  what 
unit  prices  may  be  paid  for  electrical  power  so  that  the  heat- 
ing cost  in  the  electric  furnace  does  not  exceed  that  of  the 
ordinary  furnace,  with  the  given  price  of  coke  and  output  per 
h.p.  day: 


Weight  of  Pig  Iron  in  24  Hours 
per  H.P. 

Allowable  Price  per  H.P.  Year  with  the  Following 
Coke  Prices  r 

kg. 

Ib. 

$3.80 

$5.71 

$7.61 

6 

13.2 

$4-88 

S7-3I 

$9-76 

8 

I7.6 

6.09 

9.14 

12.19 

10 

22.  0 

7.61 

11.42 

15-23 

12 

26.4 

8-57 

12.85 

17.14 

By  calculation  we  obtain  the  following  table,  taking  the 
h.p.  year  as  equalling  0.736  kw.  year,  and  the  year  as  containing 
365  days: 


Weight  of  Pig  Iron  in  24  Hours 
per  Kw. 


Allowable  Price  per  Kw.  hr.  in  Cents  with  the  Following 
Coke  Prices: 


kg. 

lb. 

$3.80 

*S.  7i 

17.61 

8.15 

18 

0.0730. 

O.I09C. 

0.1450. 

10.9 

24 

.090 

•135 

.183 

13-6 

30 

.114 

.171 

.226 

16.3 

36 

.128 

.192 

.257 

In  order  to  be  able  to  form  an  opinion  from  the  figures  given 
in  the  table,  it  is  naturally  necessary  to  know  what  efficiency  is 
possible  today  with  the  electric  pig-iron  furnace,  per  kw.  day. 
This  naturally  depends  in  the  first  place  on  the  quality  of  the 
ore  used.  In  the  following  chapters  the  metallurgical  part  of 
this  work  will  be  gone  into,  but  the  table  already  shows  that  with 


THE  MATERIALS   USED  IN  FURNACE  CONSTRUCTION         311 

coke  at  a  relatively  high  price,  the  price  for  electricity  must 
be  very  low  for  the  electric-shaft  or  pig-iron  furnace  to  compete 
with  the  ordinary  one.  In  Germany,  therefore,  the  electric- 
shaft  furnace  apparently  has  no  future.  This  is  clearly  shown 
in  the  following  table  by  Neumann  (Stahl  und  Eisen,  1904,  p. 
143).  Here  the  carbon  necessary  for  the  reduction  of  the  various 
ores  used  in  Germany,  and  that  replaceable  by  electric  power  is 
calculated  and  given  in  money  value.  The  price  of  coke  is  taken 
as  $3.57  per  metric  ton,  and  that  of  power  as  o.238c.  per  kw.  hr., 
or  $19.04  per  h.p.  year. 


Carbon 

The  Carbon  Replaceable  by  Elec- 
trical Energy 

In- 
creased 

Iron  Ore 

Pig  Iron 

Neces- 

Re- 

Corresponds 

Costs 

Cost  of 
Elec- 

sary  for 
Reduction 

placeable 
by  Kw.  hr. 

Coke 

Kw. 
Hr. 

Coke 

Kw. 
Hrs. 

Heat- 
ing 

Bi'bas  brown 

Bessemer 

722.9  Ib. 

1197.1  Ib. 

1400.5  Ib. 

$2,579 

$2.269 

$7.881 

$5-590 

iron  ore 

iron 

327.9  kg. 

543.     kg. 

635.3  kg. 

Dillen- 

Foundry 

910.5  Ib. 

1247.8  Ib. 

1460.0  Ib. 

$2,688 

$2.364 

$8.190 

$5.826 

b  ur  ge  r 

iron 

413.0  kg. 

566.     kg. 

662.3kg. 

Luxem- 

Basic 

509.3  Ib. 

1261.0  Ib. 

1475.7  Ib. 

$2,717 

$2.390 

$8.281 

$5.890 

burg  Loth- 

Bessemer 

231.0  kg. 

572.     kg. 

669.2  kg. 

ringen  Min- 

ette 
Swedish 

Basic 

1067.0  Ib. 

806.9  Ib. 

944.1  Ib. 

$1,636 

$1.528 

$4-985 

$3-457 

Magnet- 

Bessemer 

484.0  kg. 

336.     kg. 

428.2  kg. 

The  next  question  is:  What  unit  prices  for  electrical  power 
are  obtainable  today?  This  has  been  treated  already  in  Chapter 
XVI  of  the  first  part  of  the  book,  and  it  is  therefore  sufficient  to 
give  here  merely  the  figures  on  which  rough  calculations  can  be 
based  with  the  use  of  water-power  o.ii9C.  and  more  per  kw.  hr. 
and  more. 

With  the  use  of  blast-furnace  gas-engines 0.3570.  to  0.7140. 

Steam  turbines  of  great  efficiency 0.7140.  and  more 

Steam-engines 0.9520. 

Overland  and  large  city  central  stations 0.9520.    " 


These  figures  show  the  values  reached  under  the  most  favor- 
able conditions.     Apart  from  these,  the  prices  naturally  depend 


312   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

very  largely  on  local  conditions,  so  that  for  more  exact  calcula- 
tions these  conditions  must  be  considered.  Further,  the  figures 
refer  to  the  delivery  of  power  at  the  generators,  so  that  for 
exact  calculations,  the  transmission  losses,  and  losses  in  stationary 
or  rotating  transformers  must  also  be  considered.  In  the  latter 
case,  for  example,  these  can  easily  amount  to  20%,  so  that  the 
cost  of  power  at  the  furnace  is  20%  higher  than  at  the  central 
station. 

We  have  now  sufficiently  considered  the  influence  of  current 
consumption  and  cost  on  the  operating  costs,  and  can  pass  on 
to  the  other  points. 

The  fluxes  necessary  for  the  operation  of  electric  fur- 
naces depend  in  the  first  place  on  the  amount  of  the  impu- 
rities in  the  charge,  and  further  on  the  desired  composition  of 
the  final  material.  Also,  on  the  method  of  carrying  out  the 
refining  process,  or  on  the  furnace  construction  or  method  of 
heating,  which  under  certain  conditions  may  bring  about  a 
special  method  of  working.  As  has  been  pointed  out  in  previous 
chapters,  lime  and  roll  scale  or  ore  are  necessary  during  the 
oxidation  stage.  During  the  deoxidation  stage,  more  lime, 
together  with  some  sand  or  fluor-spar,  are  used  to  make  it  liquid, 
and  some  powdered  carbon  or  ferro-silicon  as  special  deoxidation 
medium.  Carbon  is  used  only  in  the  Heroult  furnace,  all  other 
arc  furnaces  and  also  the  Rochling-Rodenhauser  using  ferro- 
silicon,  so  that  in  these  latter  furnaces  a  somewhat  higher  ferro- 
silicon  consumption  has  to  be  figured  upon  than  in  the  Heroult 
furnace. 

Further,  all  furnaces  working  with  carbon  electrodes  use  a 
slightly  greater  amount  of  oxidizing  agents  during  the  oxida- 
tion period  when  compared  with  induction  furnaces,  which  is 
due  to  the  reducing  action  of  the  carbon  vapor.  This  must 
be  reckoned  with,  altogether  apart  from  an  increased  power 
consumption. 

The  wages  or  labor  costs  which  are  required  for  the  operating 
of  electric  furnaces,  calculated  per  ton  of  steel,  are  the  smaller 
the  greater  the  capacity  of  the  furnace  and  the  larger  the  amount 


THE    MATERIALS    USED    IX    FURNACE    CONSTRUCTION        313 

of  steel  produced.  In  almost  all  cases  the  labor  necessary  to 
operate  a  small  furnace  will  be  completely  satisfactory  to  operate 
a  larger  one.  If  we  consider  that  the  size  of  the  various  types 
of  furnaces  is  the  same,  then  the  labor  necessary  for  the  purely 
metallurgical  work  can  be  taken  as  equal  in  amount.  It  should 
be  determined  whether  solid  or  liquid  charges  are  to  be  worked, 
and  in  the  former  case  the  kind  and  amount  of  scrap  to  be  charged, 
as  well  as  the  kind  of  auxiliary  machinery  to  be  used.  If  we  also 
suppose  that  the  number  of  men  necessary  to  handle  molds  and 
work  on  ladles  is  the  same  under  all  conditions,  for  the  different 
furnaces,  (which  appears  to  be  absolutely,  correct,)  then  the 
same  amount  of  labor  would  be  used  with  all  the  furnaces  for  the 
purely  metallurgical  work. 

We  have  already  noticed,  however,  in  the  first  part  of  the 
book  that  with  the  Stassano  furnace  one  man  is  necessary  to 
watch  continuously  the  electrical  recording  instruments,  and 
to  regulate  the  electrodes  according  to  their  readings.  Such  a 
man  is  necessary  with  all  arc  furnaces  unless  they  are  provided 
with  automatic  regulating  arrangements,  and  even  if  these  are. 
present  a  continuous  supervision  of  the  electrical  conditions  is 
necessary  while  the  scrap  is  being  melted,  for  example  in  the 
Heroult  furnace,  as  has  been  already  pointed  out  in  Chapter  VIII. 
This  extra  man  is  unnecessary  with  induction  furnaces,  and 
with  proper  design  of  the  furnace  all  the  switches  and  regulation 
devices  can  be  looked  after  by  the  first  melter  without  any  great 
or  important  waste  of  time. 

When  working  with  fluid  charges  in  arc  furnaces  equipped 
with  automatic  regulation  no  important  switching  work  is  neces- 
sary, and  the  special  expense  can  be  saved.  These  conditions 
are  not  without  bearing  on  the  amount  paid  for  labor  per  ton  of 
steel. 

The  lining  and  repair  costs  form  a  very  important  part  of 
all  operating  costs.  They  include  labor  and  the  expense  of 
material.  The  material  costs,  in  the  first  place,  depend  largely 
on  local  conditions  so  that  correct  unit  prices  cannot  be  given. 
Apart  from  this  the  wear  and  tear  on  the  furnace  roof  and  walls 


314    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

depend  very  largely  on  the  method  of  heating.  For  this  reason 
we  find,  for  example,  that  the  roof  is  strongly  attacked  in  all 
arc  furnaces,  as  it  is  exposed  to  the  heat  radiated  from  the  arc, 
while  an  attack  on  the  roof  of  induction  furnaces  can  scarcely  be 
noticed.  The  reason  is  that  in  the  latter  case  the  heat  is  pro- 
duced in  the  metal  bath  itself  so  that  the  roof  is  protected  by 
the  covering  of  slag,  altogether  apart  from  the  fact  that  at  no 
place  is  a  temperature  of  3,500  C.  produced,  as  is  sometimes  the 
case  near  the  carbon  electrodes. 

In  all  electric  furnaces  there  is  also  a  certain  wearing  away 
of  the  dolomite  or  magnesite  hearth  by  the  slag.  As  long  as 
possible  this  is  taken  care  of  by  repairs  made  between  the  charges. 
This  is  done  the  more  easily  if  all  parts  of  the  hearth  can  be 
reached  from  the  doors,  and  if  the  material  used  sticks  to  the 
places  to  be  repaired.  The  cylindrical  Heroult,  Rennerfelt, 
Girod,  and  Stassano  furnaces,  as  well  as  the  Rochling-Roden- 
hauser,  only  allow  such  repairs  to  a  certain  extent,  so  that  after 
a  run  of  a  certain  number  of  charges  the  furnaces  must  be  stopped 
for  repairing  the  walls,  and  in  the  case  of  the  Girod,  Gronwall, 
etc.,  the  bottom  also.  This  brings  about  a  certain  loss  of  time 
and  expense  for  labor,  both  of  which  are  the  greater,  depending 
on  the  difficulty  of  making  the  walls  and  roofs.  The  Stassano 
shows  the  most  unfavorable  conditions  in  this  respect,  while 
the  Girod  and  Rochling-Rodenhauser  can  be  prepared  for  opera- 
tion in  about  the  same  time.  Furnace  linings  last  anywhere 
between  6  and  600  heats,  averaging  about  100. 

In  regard  to  furnace  repair  costs  it  is  evident  that  with 
arc  furnaces  the  price  of  material  for  the  roof  as  well  as  the 
hearth  is  of  determining  influence,  while  for  induction  fur-, 
naces  the  latter  alone  is  of  special  importance.  In  general  it 
may  be  said  that  the  repair  and  maintenance  costs  of  the 
furnaces  mostly  used,  namely,  the  Heroult,  Girod,  and 
Rochling-Rodenhauser,  do  not  exceed  those  of  the  open  hearth, 
as  soon  as  heats  averaging  3  tons  and  upwards  are  worked. 
In  open-hearth  furnaces  this  can  be  taken  as  36  to  6oc.  per 
ton,  under  normal  conditions. 

The  depreciation  is  naturally  higher,  the  more  expensive  the 


THE   MATERIALS   USED   IN  FURNACE   CONSTRUCTION         315 

whole  plant  having  the  same  capacity.  It  is  therefore  important 
to  use  the  plant  as  completely  as  possible,  and  the  induction 
furnace  allows  this  the  most  easily,  as  it  works  without  rapid 
current  variations.  As  this  furnace  moreover  has  undoubtedly 
the  best  working  efficiency,  and  can  be  kept  under  current 
continuously,  even  during  charging,  without  the  machinery 
being  in  danger,  there  is  a  saving  in  time,  and  therefore  an 
increase  in  production  for  a  given  size  of  furnace. 

With  an  equal  amount  of  total  plant  cost  the  deprecia- 
tion per  ton  of  steel  with  the  induction  furnace  must  be  smaller 
than  with  other  electric  furnaces.  In  regard  to  the  extent 
of  the  cost  of  plant  itself,  the  first  part  of  the  book  may  be 
referred  to. 

Electrode  Costs.— This  comes  into  question  only  with  arc 
furnaces.  The  conditions  affecting  the  consumption  of  electrodes 
were  treated  in  Chapter  VI  of  the  first  part  of  the  book.  It 
was  also  proved  in  Chapter  IX  that  the  Girod  and  Heroult 
furnaces  should  be-  considered  as  working  with  the  same  electrode 
conditions,  provided  that  both  furnaces  are  technically  of  the 
same  excellence.  We  can,  therefore,  without  further  thought 
put  down  the  electrode  consumption  in  these  two  furnaces  as 
equally  high.  Oh  the  other  hand  the  Stassano  furnace,  working 
under  altogether  different  conditions,  will  give  another  electrode 
consumption.  The  electrode  material  will  also  naturally  affect 
the  cost  per  ton  of  steel.  Carbon  electrodes  vary  in  price  from 
$115.71  to  $200  per  metric  ton;  graphite  electrodes,  $253.90 
to  $400.  Graphite  electrode  consumption  varies  between  2  and 
13.6  kg.  (4.4  and  30  lb.),  and  amorphous  carbon,  between  13.6 
and  27.2  kg.  (30  and  60  lb.)  per  metric  or  gross  ton  of  steel 
made,  exclusive  of  breakages.  Specific  cases  are  given  later  on. 

It  is  perhaps  not  without  value  to  consider  that  the  mild 
steel  pole. pieces,  such  as  are  used  in  the  Rochling-Rodenhauser 
furnaces,  are  not  attacked.  As  is  well  known  they  are  protected 
from  the  high  temperatures  of  the  bath  by  a  conductor  of  the 
second  class,  which  is  composed  of  the  lining  itself.  Through 
this  arrangement  every  electrode  cost  disappears. 

Certain  operating  costs  proceed  from  the  auxiliary  machinery 


316   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

necessary  with  all  furnaces.  For  instance,  with  the  Rochling- 
Rodenhauser  furnace  there  is  the  air  cooling  of  the  transformers, 
and  with  all  arc  furnaces  a  certain  water  consumption  for  cooling 
the  electrodes,  or  for  the  governing  of  the  electrodes  as  in  the 
Stassano  furnace.  To  this  also  belong  the  costs  of  the  power 
necessary  for  the  tilting  or  turning  of  the  furnaces,  and  finally 
also  that  necessary  for  automatic  regulation,  etc.  These  costs 
altogether  are,  however,  only  very  small.  With  all  electric 
furnaces  they  only  amount  to  a  very  few  cents  per  ton.  Finally 
a  certain  consumption  of  working  tools,  rabbles,  rods,  etc.,  should 
not  remain  unmentioned,  which  should  cause  about  the  same 
costs  for  all  furnaces.  Also  when  calculating  the  costs  exactly, 
the  power  for  lighting,  operating  the  travelling  cranes,  etc., 
should  be  considered,  which  can  be  taken  as  equally  high  for  the 
different  furnaces.  Finally,  there  is  a  license  cost  which  comes 
into  question,  concerning  the  amount  of  which  only  the  companies 
owning  the  patents  can  give  information. 

As  a  conclusion  some  operating  costs  may  be  given  for 
different  furnaces.  It  should  be  again  pointed  out  that  such 
figures  and  comparisons  are  to  be  used  with  the  greatest  care 
because  they  are  based  altogether  on  local  conditions,  and  also 
on  the  kind  of  metal  charged  and  obtained.  In  regard  to  the 
operating  costs  of  the  electric  shaft  furnace  it  has  been  pointed 
out  already  that  it  can  only  compete  with  the  ordinary  blast 
furnace  under  the  most  favorable  conditions.  These  conditions 
exist,  for  instance,  in  some  parts  of  the  United  States,  Canada, 
Norway,  Sweden,  Japan,  and  Switzerland,  and  the  following 
comparison  of  costs  is  for  Sweden. 

It  has  been  made  by  Prof,  von  Odelstierna  of  Stockholm,  and 
is  taken  from  the  Electro  Chemical  and  Metallurgical  Industry, 
1909,  p.  420. 

In  the  charcoal  blast  furnace: 

0.950  metric  tons  charcoal  at  $8.00  per  ton $7 . 60 

Labor i .  oo 

Repairs  and  general  expenses i .  50 


Per  metric  ton #10. 10 


THE   MATERIALS   USED  IN  FURNACE   CONSTRUCTION         317 

In  the  electric  shaft  furnace: 

O.  270  metric  tons  charcoal $2.16 

0.3  electric  h.p.  years  at  $12.142 3 . 60 

Labor x  oo 

10  Ib.  electrodes  at  3c.  Ib 30 

Repairs  and  general  expenses 1 . 50 


Per  metric  ton $8 . 56 

According  to  these  figures  the  use  of  the  electric  furnace 
gives  a  gain  of  about  $1.54.  It  is  based  on  the  assumption  that 
the  Gronwall,  Lindblad  &  Stalhane  furnace,  which  has  shown 
up  the  best  so  far,  is  taken  as  the  electric  shaft  furnace.  The 
ore  taken  for  the  comparison  ought  to  contain  60%  metallic 
iron,  and  the  charcoal  83%  carbon. 

It  is  further  assumed  that  both  furnaces  have  the  same 
output — from  8000  to  10,000  metric  tons  per  year.  The  prices 
for  ore  and  raw  limestone*  are  not  taken  into  consideration,  as 
they  depend  so  largely  on  local  conditions. 

If  we  compare  the  results  found  here  with  the  previously 
given  table  of  the  cost  of  current  for  the  electric  blast  furnace, 
we  find  complete  agreement.  For  instance,  from  the  table  on 
page  290,  we  see  that  if  the  cost  of  heating  in  the  two  types  of 
furnace  is  to  be  equally  great  the  h.p.  year  should  cost  $12.19. 
This  is  with  a  production  of  (8  kg.),  17.637  Ib.  pig  iron  per  h.p. 
day,  and  a  price  of  coke  of  $7.61  per  metric  ton.  The  figures 
of  Prof,  von  Odelstierna  are  based  on  power  at  $12.14  per  h.p. 
year,  charcoal  at  $8.09  per  metric  ton,  and  an  output  of  i  metric 
ton  per  0.3  h.p.  year.  This  corresponds  to  about  (9  kg.),  19.841 
Ib.  per  h.p.  day.  If  it  is  assumed  that  the  coke  and  charcoal 
contain  the  same  carbon  then  the  estimate  of  von  Odelstierna  is 
calculated  with  a  higher  output  and  with  a  greater  price  for 
carbon,  both  of  which  points  are  favorable  to  the  operating  costs 
of  the  electric-blast  furnace. 

It  should,  however,  be  again  pointed  out  that  such  favorable 

*  In  the  Metallurgical  and  Chemical  Engineering,  Feb.,  1912,  p.  71, 
LEFFLER  says  that  in  practise  it  has  been  found  more  economical  to  use 
unburned  limestone,  and  that  among  other  things  burned  limestone  causes 
the  burden  to  hang. 


318      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

conditions  for  the  electric-shaft  furnace  are  not  often  present, 
so  that  it  is  restricted  to  countries  poor  in  fuel  and  rich  in  ore 
and  electricity. 

In  this  respect  it  is,  however,  encouraging  to  note  that,  after 
the  five  months'  test  made  at  Trollhattan,  ending  April,  1911, 
(according  to  The  Iron  and  Coal  Trades  Review,  of  Nov.  10,  1911), 
the  pig  iron  produced  per  h.p.  year  equalled  3.79  metric  tons  or 
22.92  Ib.  (10.41  kg.)  per  h.p.  day;  this  corresponds  to  an  output 
of  i  metric  ton  per  .262  h.p.  year.  These  later  and  better  figures 
are  the  average  of  the  first  week's  run  after  again  starting  up, 
and  are  attributed  to  the  improved  gas  circulation,  under  the 
furnace  roof  which,  according  to  Robertson,  the  inventors  main- 
tain that  the  important  point  is  to  make  this  furnace,  last  as 
long  as  possible,  and  in  order  to  do  this  they  consider  it  absolutely 
necessary  to  have  the  roof  cool.  Richards  suggests  (A.E.S., 
April,  1912)  that  the  arch  of  the  furnace  hearth  be  protected 
by  water-cooled  plates,  as  is  common  with  open-hearth  practise. 
This,  however,  as  has  already  been  suggested,  may  decrease  the 
efficiency  too  much.  Lyon  states  that  attempts  were  made  at 
the  Noble  Electric  Steel  Co.  in  California  to  preserve  the  roof 
of  the  crucible  hearth  by  water-cooled  plates  embedded  in  the 
brickwork,  but  these  did  not  prove  especially  effective.  Leffler 
writes  at  this  time  that  they  would  gladly  dispense  with  the 
artificial  gas  circulation  if  they  could.  As  is  elsewhere  men- 
tioned, Leffler  says  that  calcined  limestone  causes  the  burden 
to  hang.  Yet  Noble,  with  his  California  furnace,  says  he  only 
uses  calcined  limestone,  and  furthermore  uses  no  artificial  gas 
circulation.*  In  the  last  tests  made  at  Trollhattan,  the  repairs 
and  petty  expenses  cost  about  $1.60  per  ton  of  pig  iron  produced. 
Part  of  these  operating  cost  repairs  are  caused  by  the  roof  burning 
away.  If  half  of  the  above  amount  were  saved  by  the  durability 
of  the  roof  being  increased,  it  would  make,  in  a  2500  h.p.  furnace, 
producing  25  tons  daily,  an  annual  saving  of  350  X  25  X  .80  = 
$7,000,  enough  to  pay  almost  9%  on  the  investment. 

*  The  reason  the  Trollhattan  furnace  has  gas  circulation  and  the '  Noble 
furnace  none,  is  because  the  former  is  operated  as  an  arc  furnace,  but  the 
latter  as  a  resistance  furnace. 


THE   MATERIALS   USED   IN  FURNACE   CONSTRUCTION         319 

The  cost  of  producing  one  ton  of  electric  pig  iron  during 
the  5  months  period  ending  in  April,  1911,  was  estimated  from 
the  records  and  from  a  personal  investigation  given  on  the  spot 
to  be  as  follows: 

1.52  tons  of  ore,  67.1%  at  $2.68 $4.07 

.262  kw.  year  at  $13.40 3-51 

85.    kg.  (187  Ib.)  limestone  at  $i.6l  per  ton 14 

416  kg.  (915  Ib.)  charcoal  at  $12. .    4.99 

5.27  kg.  electrodes  consumed  *  at  $67 36 

Labor 78 

Repairs  and  petty  expenses 1 . 60 

Interest  and  sinking  fund,  10%  on  $24,000 35 

Total $15.80 

The  cost  of  producing  one  ton  from  hematite  of  50%  iron  was 
$16.04.  One  of  the  Norwegian  companies  on  the  West  coast, 
now  (1912)  constructing  a  plant  for  the  smelting  of  60%  magne- 
tite, estimated  the  cost  per  ton  of  iron,  with  electricity  at  $5.46 
a  kw.  year,  at  $11.25,  using  English  coke  at  $5.63  per  ton. 

For  the  Stassano  furnace  detailed  cost  figures  are  given  by 
Osann  in  Stahl  und  Risen,  1908,  No.  19.  They  apply  to  the 
furnace  described  in  Chapter  VII  for  one-ton  charges,  making 
steel  for  castings  from  cold  material.  The  figures  are  further 
based  on  the  following  special  conditions.  The  furnace  remains 
unused  each  night  for  three  hours,  and  24  hours  on  Sunday. 
During  these  times  it  is  kept  warm  by  electricity,  the  current 
being  switched  on  for  one-quarter  of  an  hour,  and  off  for  three- 
quarters  of  an  hour.  Under  this  non-continuous  operation  the 
furnace  gives  3.5  metric  tons  per  day,  or  840  metric  tons  per  year 
of  240  working  days. 

The  furnace  takes  three  men  per  shift,  the  average  wage  being 
given  as  $1.19.  The  lining  costs  $95.24,  exclusive  of  the  labor, 
when  magnesite  is  used.  It  must  be  renewed  every  three  weeks, 
that  is,  after  a  production  of  about  63  metric  tons,  and  requires 
4  to  6  days  for  the  renewal. 

*  The  total  electrodes  used  per  ton  of  iron  produced  was  10.28  kg.,  the 
difference  being  attributable  to  the  stub  ends,  now  no  longer  prevalent,  with 
the  new  screw  type  electrode. 


320     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  construction  cost  of  the  furnace  is  given  as  $8,750. 
Under  these  conditions  the  following  calculations  are  given 
per  metric  ton  of  fluid  metal: 

Depreciation $  o .  992 

Cost  of  the  charge : 

I  metric  ton  scrap  at  $15.95 $I5-952 

.02  metric  ton  mill  scale  at  $4.047. ...  .081 

.02  "  "  lime  at  $2.857 057 

.008  "  "  12%  ferro-silicon  at 

$35-71 285 

.004  "  "  8o%ferro-manganeseat 

$52.38 209 

.0008  "  aluminum  at  $357.00 ..  .285 

16.869 

Cost  of  power: 

For  melting  900  kw.  hrs.  at  i.O7ic $9.643 

For  heating  during  delays i  .071 

Cost  of  furnace,  lining,  and  repairs 2.619 

Labor 2 . 047 

Electrodes .  595 

Cooling  water .  095 


16.070 
Total $33-941 

According  to  a  more  recent  article  (Neumann,  Stahl  und 
Risen,  1910,  p.  1066)  it  is  possible  to  greatly  reduce  the  cost. of 
the  lining  when  using  dolomite  for  the  hearth.  At  the  same 
time  through  the  use  of  a  purer  charge  the  power  consumption 
for  melting  drops  to  750  kw.  hrs.,  and  because  of  the  correspond- 
ingly less  work  with  slags  the  furnace  can  last  70  to  100  heats. 
Definite  figures  for  the  lowering  in  costs  brought  about  in  this 
way  are  not  known. 

Cost  calculations  for  the  Heroult,  Rennerfelt,  Snyder  and 
Girod  furnaces,  have  been  published.  The  following  are  taken 
from  Stahl  und  Risen,  1908,  p.  1825,  and  apply  to  a  2-ton  Girod 
furnace. 


THE   MATERIALS   USED  IN  FURNACE  CONSTRUCTION        321 

If  a  cold  charge  is  worked,  consisting  of  scrap,  turnings,  and 
pig  iron,  and  completely  refined  to  give  steel  of  high  value,  the 
costs  per  metric  ton  are  as  follows: 

.1  ton  lime,  .1  ton  ore,  and  additions  of  various 

alloys,  from $   .71410$   .809 

Electrodes 952  -     i .  190 

Labor 1. 142 

Furnace  maintenance,  tools,  etc 2 . 857 

1,000  kw.  hrs.,  the  cost  depending  on  the  price 
of  power 

If  melting,  without  further  refining,  is  all  that  is  necessary, 
that  is  to  say  a  similar  method  of  working  to  that  recently  car- 
ried out  with  the  Stassano  furnace  at  Bonn,  then  the  following 
figures  should  be  used: 

Lime,  etc $0.238 

Electrodes 762 

Labor 762 

Furnace  maintenance,  tools,  etc 2 . 285 

Power  consumption,  750  kw.  hrs 

For  the  refining  of  a  liquid  steel  charge  taken  from  the  con- 
verter or  open  hearth,  the  following  figures  are  given: 

.04  tons  lime,  and  additions $  .  524  to  $  .619 

Electrodes .381 

Labor .571 

Furnace  maintenance,  etc .952 

Power  consumption  about  300  kw.  hrs 

In  these  tables  depreciation  and  the  loss  in  operation  have 
not  been  taken  into  consideration. 

The  latter  is  given  by  Borchers  as  10  to  11%,  who  also  says 
that  the  consumption  of  electrodes  in  the  larger  furnaces  ought 
to  amount  to  0.012  to  0.015  metric  tons  per  metric  ton  of  steel 
with  cold  charges.  This  gives  an  electrode  cost  of  $0.571  to 
$0.762  per  metric  ton.  In  regard  to  the  life  of  the  Girod  furnace 
it  is  stated  that  with  cold  charges  the  walls  last  about  80,  and 
the  bottom  about  120  heats,  the  roof  stands  25  to  30  heats  with 
small  furnaces  and  20  to  25  with  large  ones. 


322       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  costs  with  the  Heroult  furnace  will  scarcely  differ  in  an 
important  degree  from  those  of  the  Girod,  except  for  the  lesser 
Heroult  bottom  costs.  For  the  Heroult  furnace  the  following 
partial  results  may  be  shown  taken  from  Metallurgical  and  Chemi- 
cal Engineering,  1910,  p.  179.  They  apply  to  the  15-ton  furnace 
at  So.  Chicago.  Liquid  Bessemer  metal,  of  which  the  composi- 
tion is  not  given,  is  refined  in  12-  to  14-ton  charges  the  final 
material  containing  0.03%  P.  and  0.03%  S.  Power  consumption 
200  kw.  hrs.  per  metric  ton.  The  furnace  roof  of  silica  brick  costs 
$60.  It  requires  changing  each  Sunday.*  With  12  heats  a  day, 
and  13  metric  tons  per  charge,  this  equals  0.0642. 

Hearth  repairs,  about $o .  0642 

Lining  costs,  about 1284  f 

This  does  not  take  into  consideration  the  costs  per  ton  of  door 
bricks,  which  must  be  replaced  at  certain  times.  The  electrode 
consumption  is  given  as  (6.6  Ib.)  3  kg.  per  metric  ton.  Graphite 
electrodes  are  used,  and  the  cost  per  ton  of  steel  is  about  $0.91. £ 

Neumann  gives  the  loss  with  a  cold  charge  as  6%,  and  2.5 
to  3%  with  fluid  charges.  With  the  same  kind  of  charge,  how- 

*  The  roof  problem  has  recently  been  the  subject  of  careful  study  by 
FitzGerald  (see  A.  I.  E.  E.,  June  25,  1912,  transactions).  A  brick  made  of 
silicon  carbide  has  been  manufactured  which  it  is  believed  will  have  a  much 
longer  life  in  the  steel  furnace  than  the  silica  brick  now  used.  The  brick  is 
made  by  taking  powdered  or  granular  silicon  carbide,  mixing  it  with  a  suitable 
temporary  binder,  such  as  a  solution  of  dextrine,  molding  and  then  heating 
in  an  electric  furnace  to  the  temperature  at  which  silicon  carbide  is  formed. 
Bricks  made  in  this  way  have  been  used  in  the  roof  of  an  experimental  steel 
furnace  in  one  of  these  laboratories  and  then  put  to  the  severest  test  possible. 
The  bottom  of  the  furnace  was  purposely  raised  well  above  the  normal  level 
so  as  to  bring  the  surface  of  the  slag  as  close  to  the  roof  as  possible,  the  actual 
distance  in  some  experiments  being  only  10  in.  (25.4  cm.).  Then  the  furnace 
was.worked  at  double  the  normal  rate  of  generation  of  energy  so  that  the  heat- 
ing of  the  roof  was  very  intense,  so  much  so  that  an  ordinary  silica  roof  would 
melt  down  rapidly  and  be  completely  destroyed  in  a  single  heat.  Even  under 
these  very  severe  conditions  the  silicon  carbide  roof  stood  up  perfectly.  Ex- 
periments have  also  been  made  in  other  steel  furnaces  and  these  results  con- 
firmed. The  most  serious  objection  to  a  roof  of  this  kind  is  its  heat  loss 
and  cost.  If  it  lasts  a  sufficiently  long  time  it  is  nevertheless  economical. 

t  Dolomite  taken  at  $6.00  per  metric  ton. 

J  This  applies  to  electrodes  of  Acheson  graphite,  costing  27  cents  per  kg., 


THE   MATERIALS   USED   IN  FURNACE   CONSTRUCTION         323 

ever,  the  same  loss  is  to  be  expected  in  both  the  Heroult  and 
Girod  furnaces. 

A  certain  difference  in  the  operating  costs  of  the  Heroult  and 
all  other  electric  furnaces  arises  from  the  fact  that  the  former 
uses  carbon  for  deoxidation  instead  of  ferro-silicon.  With  nor- 
mal heats,  therefore,  and  deoxidation  with  carbon  the  Heroult 
furnace  has  to  figure  on  a  consumption  of  about  4  kg.  ferro-silicon 
per  metric  ton;  in  the  case  of  other  furnaces,  and  the  Heroult 
also,  if  deoxidation  with  carbon  is  not  followed,  on  about  7  kg. 
If  it  is  assumed  that  the  Heroult  uses  3  kg.  petroleum  coke, 
then  the  following  figures  are  given  for  deoxidation  and  de- 
sulphurization: 

Heroult  furnace,  using  3  kg.  petroleum  coke  at  $1.90. . .  $0.057 
Heroult  and  all  other  furnaces  using  3  kg.  ferro-silicon 

at  7.260. «. 216 


So  that  deoxidation  and  desulphurization  by  means  of 
ferro-silicon  alone  is  dearer  than  that  by  carbon  and 
ferro-silicon  by  about 159 

This  is  with  50  per  cent  ferro-silicon  costing  about  $74  per 
metric  or  per  gross  ton.  With  this  alloy  costing  considerably 
more  than  the  figure  mentioned  above,  even  though  the  price  of 
petroleum  coke  increases  correspondingly,  and  even  more  so, 
the  demarcational  advantage  of  refining  with  carbon  instead  of 
with  ferro-silicon  becomes  more  apparent.  From  an  operating 
standpoint,  however,  it  is  a  little  easier  to  achieve  results  with 
a  more  expensive  method. 

As  mentioned  before,  this  has  the  advantage,  however,  that 
it  does  not  influence  the  composition  of  the  bath,  and  so  is  often 
used  even  in  the  Heroult  furnace. 


such  as  are  used  in  this  furnace.  Up  to  within  a  short  time  it  was  impossible 
to  construct  satisfactory  electrodes  of  carbon  for  the  15- ton  Heroult  furnace. 
These  are  the  20"  round  amorphous  carbon  electrodes.  Ever  since  February, 
1913,  Howland  advises  that  12"  diameter  Acheson  Graphite  are  being  used 
with  success  in  these  furnaces  with  only  one  breakage  in  67  used,  and  that 
the  cost  per  ton  of  molten  metal  refined  is  no  more  than  with  the  larger 
amorphous  carbon  electrodes. 


324      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Advice  is  received  from  Gray  (J.  H.)  that  with  a  6-ton  basic 
Heroult,  operating  24  hrs.  daily  and  6  days  weekly,  with  elec- 
tricity at  one  cent  per  kw.-hr.,  the  cost  of  refined  steel,  one  or 
two  slags,  should  on  the  average  not  be  over  $15  per  ton,  plus 
the  cost  of  scrap,  in  normal  times. 

There  remain  finally  the  operating  costs  of  the  Rochling- 
Rodenhauser  furnaces.  Such  figures  have  been  published  by 
Wedding.  The  following  apply  to  a  5-ton  furnace  working  on 
fluid  charges: 

Power  consumption  230-280  kw.-hrs.  per  metric  ton 

Additions,  about $o. 536 

Lining  costs,  using  magnetite 595 

Wages 178 

Air  for  cooling  transformers 050 

A  2-ton  furnace  using  polyphase  current  gave  the  following 
costs,  when  scrap  was  worked  up  for  making  steel  castings: 

Charge 

i  metric  ton  scrap $15-952 

5%  loss 798 

.01     metric  ton  roll  scale (22.    Ib.) 040 

.035       "         "    lime (77.    Ib.) 100 

.005       "         "    fluor-spar (15.7  Ib.) 074 

.01  "    sand (22.    Ib.) 014 

.004  "    ferro- manganese (  8.8  Ib.) 209 

Loss  in  ferro-alloys  remaining  behind 157 


$17-344 
Power  consumption,  about  900  kw.-hrs.,  price  varies. 

Lining  and  repair  costs 636 

Labor 793 

Air  for  cooling  transformers  at  i.O7ic.  per  kw.-hr 079 

These  figures  are  given  for  a  2-ton  furnace  which,  working 
with  cold  charges,  allows  a  production  of  6  to  8  tons  per  day. 
Apart  from  this  it  should  be  mentioned  that  the  lining  and 
repair  costs  when  dolomite  is  used,  and  liquid  charges,  only 
amount  to  0.238  to  o.428c.  with  3-  to  8-ton  furnaces. 

It  may  be  mentioned  again  that  all  the  cost  figures  given 
above  are  only  exactly  correct  for  certain  predetermined  local 


THE  MATERIALS   USED  IN  FURNACE   CONSTRUCTION         325 

conditions.  Care  should,  therefore,  be  taken  in  using  them  for 
comparison.  The  weight  of  material  used  ought  to  be  known, 
and  the  kind  of  charge  and  the  final  metal  required  have  a  great 
influence. 

The  consideration  of  the  different  factors  affecting  costs  given 
in  the  first  part  of  the  book  appears,  therefore,  to  be  very  valuable, 
and  this  part  may  once  again  be  referred  to. 


B.  THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL 
INTRODUCTION 

UNTIL  the  invention  of  the  steam-engine  the  operation  of  an 
iron  and  steel  plant  required  the  presence  of  a  waterfall  as  the 
source  of  power  for  the  hammers  and  blast.  If,  at  the  same  time, 
sufficient  ore  beds  and  forests  were  in  the  neghborhood  all  the 
requirements  were  filled  for  the  prosperity  of  the  plant.  The 
consumption  of  iron  and  steel  tools  was  moderate,  the  plants 
could  operate  economically  in  a  modest  way  and  with  small 
water-powers,  for  with  the  absence  of  railroads,  etc..  the  products 
found  a  paying  market  in  the  immediate  vicinity,  and  the  bring- 
ing in  of  foreign  goods  was  almost  impossible.  The  few  specially 
large  German  water-powers  were  not  needed,  and  would  not  be 
used  because  the  technical  knowledge  necessary  was  not  sufficient- 
ly advanced. 

Conditions  changed  as  the  supply  of  charcoal  began  to  de- 
crease and  the  consumption  of  iron  and  steel  to  increase,  for  the 
old  plants  with  their  associated  water-powers  and  limited 
amounts  of  charcoal  could  only  increase  their  production  to  a 
certain  amount.  The  knowledge  that  ores  could  be  smelted  with 
coke,  and  the  invention  of  the  steam-engine,  made  it  possible  to 
use  commercially  the  immense  stores  of  energy  lying  dormant  in 
the  earth  in  the  form  of  coal.  Soon  the  plants  deserted  their  old 
places  near  the  waterfalls,  and  changed  their  locations  to  the 
coal-fields,  where  fuel  and  therefore  power  were  present  for 
application  in  unlimited  amounts. 

Then  succeeded  the  remarkable  newer  growth  of  the  iron 
and  steel  industry  with  its  attendant  immense  production. 

But  the  consumption  of  iron  and  steel  constantly  increases, 
coal  begins  to  decrease  in  amount  and  become  more  expensive, 
and  the  industry  will  soon  be  forced,  as  in  the  time  of  our  fathers, 
to  look  for  a  new  and  constant  source  of  power.  Electric  energy 


THE   ELECTRO-METALLURGY  OF  IRON  AND   STEEL          327 

is  the  first  to  come  into  consideration,  since  it.  is  possible  to  pro- 
duce .it  from  coal  at  a  moderate  cost.  Also  the  railroads  have 
brought  the  most  remote  countries  into  connection,  and  the 
enormous  water-powers  of  foreign  lands  can'  be  used  as  sources 
of  cheap  electric  power.  Is  it  to  be  wondered  at  that  many 
technical  men  are  working  at  the  problem  of  the  building  of 
electric  furnaces,  or  that  this  task  should  soon  be  solved  economic- 
ally, when  it  is  known  that  electric  heating  produces  a  higher 
furnace  efficiency  than  heating  with  fuel? 

So  we  see  efforts  being  made  recently  to  build  plants  near 
the  larger  water-powers,  as  in  the  old  days,  in  order  to  obtain 
electric  power  at  the  lowest  cost,  and  to  produce  iron  and  steel 
from  ore  by  electricity. 

Also  in  the  industrial  countries  the  electric  furnace  is  gaining 
importance  from  day  to  day,  for  it  is  proving  capable  of  pro- 
ducing higher  quality  steels  equal  to  crucible  steel,  from  impure 
raw  material. 

It  is  the  authors'  wish  that  the  production  of  iron  and  steel 
by  electricity  may  receive  such  an  impulse  that  the  statements 
in  this  little  book  will  very  soon  be  exceeded  by  the  facts. 

GLUCK  AUF! 

J.  SCHOENAWA. 


THE  ELECTRIC  SMELTING  OF  IRON  ORES  FOR  IRON 
AND  STEEL  PRODUCTION 

The  usual  commercial  process  by  which  pig  iron  is  produced 
is  smelting  in  a  blast  furnace  with  fuel,  flux  .and  a  blast  of  air. 
In  the  upper  part,  or  shaft,  of  this  furnace  a  continuous"  series 
of  thermal  and  chemical  reactions  take  place,  which  reduce  the 
iron  and  prepare  it  for  its  final  smelting  in  the  hearth.  These 
preliminary  reactions  could,  if  desired,  be  carried  on  in  a  special 
shaft  into  which  ore  is  charged  and  subjected  to  the  action  of 
the  hot  furnace  gases. 

In  the  lower  part,  or  smelting  zone,  of  the  furnace  the  reduced 
and  partially  carburized  iron  is  melted;  the  impurities  of  the 
ores  and  fuel  are  fluxed  with  the  flux  added  for  this  purpose,  and 
thereby  converted  into  a  liquid  cinder,  or  slag.  Besides  these 
thermal  effects,  some  chemical  reactions  occur  which  the  temper- 
ature in  the  shaft  was  not  sufficiently  elevated  to  effect,  such  as 
the  reduction  of  the  oxides  of  silicon,  manganese  and  phosphorus 
(the  reduced  elements  being  then  absorbed  by  the  iron),  the 
conversion  of  iron  sulphide  in  part  to  calicum  sulphide,  etc. 

First  let  us  collect  the  data  upon  which  to  base  a  study  of 
these  reactions.  Such  data  are  given  below;  some  of  them  have 
not  been  wholly  confirmed  experimentally,  yet  .the  estimated 
values  are  close  enough  to  afford  calculations  of  practical  value: 

i  kw.  hr.  =  864.5  calories, 
i  kw.  hr.  =  1.34  h.p.  hrs. 
i  h.p.  hr.  =  0.746  kw.  hrs. 
Spec.  ht.  of  iron  =  0.20. 
Spec.  ht.  of  blast  furnace  slags  =  0.30. 
Spec.  ht.  of  ore  =  0.20. 
Spec.  ht.  of  CO  =  0.243. 
Spec.  ht.  of  C  =  0.20. 

Spec.  ht.  of  air  according  to  its  weight  =  0.30. 
Latent  heat  of  fusion  of  pig  iron  =  46  calories. 
Latent  heat  of  slag  =  30  calories. 
328 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  320 


PLATE   I. 

Test   pieces   of   seamless   drawn  electric   steel   tubes    (Rochling).     The 
normal  tube,  and  test  pieces  made  from  it  in  the  cold  state. 


330    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

TABLE  I 


WITH  THE  REDUCTION  OF  i  KG.  OF  REDUCED  MATERIAL 

IS   NECESSARY 

IS   OBTAINED 

HEAT   REQUIRED 

C.  kg. 

CO  kg. 

CO  kg. 

COzkg. 

Gain 

cals. 

Loss 
cals. 

Balance 
cals. 

FeO+C=Fe+CO.. 
FeO+CO  =  Fe-|-CO2 
Fe3O4  +  4C=3Fe  + 
4CO  

0.2I4 
(0.2  14) 

0.286 

=0.500 

0.500 

0.786 

529 
1,200 

•    707 
1,603 

795 

1,802 
1,078 
719 

540 
2,119 

2,394 

1,332 
1,332 

l,648 

i,648 
1,876 

1,876 
2,209 
1,947 

1,817 
7,829 

5,966 

-    803 
-    132 

-  941 

-     45 
—  1081 

-     74 
-1131 
-1228 

-1277 
-57io 

-3572 

0.667 

Fe3O4  +  4  CO  =  3Fe 
+4CO2  

(0.286) 

0.321 

(0.321) 
0.436 
0.291 
0.218 

0.857 

0.968 

=0.667 
=0.75 

.509 

1.048 
I.I78 

Fe2O3+3C=2  Fe  + 

3co 

0-75 

1.017 
0.679 
0.509 

2.OO 
2.258 

Fe,O3+3CO=2Fe+ 
3CO:i   

MnO2+2C=  Mn  + 

2CO  

Mn304+  4C  =  3Mn 

+4co 

MnO  +  C  =  Mn  + 
CO  
SiOa+2C  =  Si+2CO 
P205  +  5C=2P  + 
SCO  

To  reduce  1000  kg.  of  iron  from  magnetite  requires  1381  kg. 
of  ore.  For  simplicity  the  ore  may  be  considered  as  pure  Fes  C>4 
without  any  earthy  constituents  which  have  to  be  slagged  off. 
Reduction  with  pure  carbon  then  takes  place  according  to  the 
following  equation:  232  kg.  Fes  (X  +  48  kg.  C  =  168  kg.  Fe  -f- 
112  kg.  CO.  The  CO  therefore  measures  4  X  22.4  =  89.6  cu. 
metres.  For  the  production  of  a  metric  ton,  1000  kg.  of  pure 
iron  286  kg.  of  carbon  are  necessary  and  533  cu.  m.  of  carbon- 
monoxide  are  produced. 

In  .the  blast  furnace  much  larger  amounts  of  carbon  than 
these  theoretical  calculations  call  for  are  required,  because 
carbon  is  depended  upon  not  only  to  reduce  the  ore,  but  also 
to  furnish  the  heat  required  for  the  process.  According  to  the 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  331 

equation  Fe3  O4  +  4C  =  3  Fe  +  4  CO,  the  process  can  be 
carried  out  without  the  blast  being  used  if  the  amount  of  heat 
is  supplied  which  the  table  shows  is  necessary.  The  amount  of 
gas  produced  by  the  reduction  would  be  only  about  one-tenth  of 
that  produced  in  the  blast  furnace  for  the  same  weight  of  iron, 
for  in  the  latter  case  the  gas  is  diluted  with  a  large  nitrogen 
content. 

If  magnetite  is  mixed  with  carbon  in  the  proportion  calculated 
above,  and  the  mixture  heated  by  electricity  to  the  necessary 
reduction  temperature  as  well  as  to  the  melting  temperature  of 
about  1300°  C.,  reduction  of  the  magnetite  takes  place  readily. 
The  following  rough  calculation  gives  the  theoretical  power 
consumption  necessary  for  the  production  of  i  metric  ton  of 
iron  in  a  condition  fluid  enough  to  be  readily  tapped,  which  is 
necessary  in  practise. 

1381  kgs.  ore  heated  to  1300°  C.  =  1381  Xo.2  X 1300  =  .  .  .   359,060  cals. 
286  kgs.  carbon  heated  to  1300°  C.=  286X0.2X1300=     74,360     " 
looo  kgs.  iron  heated  to  reducing  temperature  1000X941  =   941,000 
lOOOkgs.  iron  melted  =  1000X46  = 46,000     " 


1, 420,420  cals. 


1420420 

This  corresponds  to-^-    —  =  1043  kw.  hrs. 
004.5 


From  this  it  is  clear  that  the  process  requires  much  less 
carbon  than  the  blast  furnace  if  considerable  electric  energy  is 
supplied.  In  the  same  manner  a  high-carbon  iron  can  be 
produced  if  sufficient  carbon  be  supplied  not  only  to  reduce 
the  ore,  but  also  to  supply  that  which  dissolves  in  the  metal. 
A  rough  calculation  for  an  iron  with  3%  carbon  is  given 
below: 

The  carbon  required  is  286  +  30  =  316  kg.,  and  1030  kg.  of 
pig  iron  is  produced. 

1,381  kg.  ore  heated  to  1300°  C 359,o6o  cals. 

316  kg.  carbon  heated  to  1300°  C 82,160 

I.ooo  kg.  iron  to  the  reducing  temperature 941,000 

1,030  kg.  iron  melted 47.3^0 

1,429,600  cals. 


332   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

This  corresponds  to  ^~ =  1653.7  kw.  hrs.  per  1030  kg. 

504.5 

iron,  which  equals  1605.5  kw.  hrs.  per  metric  ton. 

It  should  be  remembered  that  the  figures  given  for  the  coke 
consumption  in  the  blast  furnace  take  in  all  losses  through 
cooling,  radiation,  etc.,  and  in  this  respect  the  efficiency  of  the 
blast  furnace  is  not  bad. 

The  power  consumption  given,  on  the  other  hand,  is  only  the 
theoretical  minimum,  in  operation  it  will  be  considerably  higher, 
depending  on  the  type  of  furnace  used  and  its  efficiency,  etc. 
Also  the  figures  for  carbon  consumption  are  for  chemically  pure 
material,  while  in  operation  fuel  containing  ash  has  always  to 
be  figured  on  so  that  the  minimum  carbon  consumption  in  the 
form  of  coke,  charcoal  or  similar  material  is  correspondingly 
higher. 

The  economical  side  of  the  smelting  of  ores  by  means  of  the 
carbon  theoretically  necessary  for  reduction  and  electrical  energy 
to  supply  the  heat  for  the  thermal  reactions  requires  that  the 
saving  in  coke  in  the  new  process  must  be  greater  than  the 
expense  of  the  necessary  electrical  energy. 

As  a  result  the  process  has  prospective  use  only  under  con- 
ditions where  ore  and  power  are  cheap  and  coke  is  dear, 
as  in  some  parts  of  Canada,  Italy,  Norway,  Sweden,  Califor- 
nia, etc. 

The  use  of  coke  can  be  completely  done  away  with  and  the 
iron  separated  from  the  ore  electrolytically  like  aluminum,  but 
the  necessary  power  consumption  is  so  extremely  high  that  this 
method  does  not  appear  economical  even  for  the  future.  Re- 
cently proposals  have  also  been  made  to  use  iron  pyrites  as  the 
raw  material  for  smelting  iron  in  the  electric  furnace.  It  is  to 
be  melted  and  air-blown  through  the  bath  until  a  consider- 
able amount  of  ferrous  oxide  has  been  formed;  then  the 
blast  stopped,  and  the  bath  allowed  to  react  according  to  the 
equation: 

FeS  +  2  FeO  =  3  Fe  +  S02 

It  is  scarcely  possible  that  the  process  will  have  a  great 
future. 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  333 

The  process  given  above  of  using  just  enough  fuel  to  combine 
with  the  oxygen  of  the  ore  and  electric  heating  of  the  ore-fuel 
mixture  forms  the  basis  of  the  many  recent  attempts  to  smelt 
iron  ore  by  electro-thermal  methods. 

It  should  be  emphasized  that,  in  electro-thermal  processes, — 
as  the  words  themselves  indicate, — the  electricity  serves  only 
as  the  source  of  heat  which  brings  the  charge  to  the  temperature 
required  for  reduction  and  melting.  Electrolytic  processes— 
where  electricity  is  used  both  as  a  source  of  heat  and  as  a  reducing 
agent — are  less  often  employed  because  only  direct  current 
can  be  used.  In  regard  to  this,  we  may  refer  again  to  Part  I. 

Electrical  heating  of  the  charge  gives  the  great  advantage 
that,  because  of  the  much  lower  fuel  consumption,  the  influence 
of  the  latter  on  the  charge  and  melted  material  can  be  regulated 
much  better,  and  the  operation  can  be  carried  out  if  desired  at 
higher  temperatures  than  used  up  to  now  in  the  blast  furnace. 
This  has  a  great  metallurgical  advantage  for,  as  is  well  known, 
the  "reaction  ability"  of  all  material  increases  considerably 
with  increase  in  temperature. 

In  general  it  is  to  be  expected  that  in  the  smelting  of  the 
ordinary  iron  ores  which  contain  more  or  less  manganese,  sulphur, 
phosphorus,  silica,  etc.,  the  same  reduction  reactions  will  take 
place  as  are  already  known  for  the  blast  furnace  process,  etc., 
and  that  with  electric  smelting  an  iron  of  a  certain  determined 
purity  and  analysis  will  be  obtained  by  regulating  the  furnace 
temperature  and  the  slag.  The  iron  will  be  very  low  in  sulphur, 
for  experience  shows  that  the  slagging  off  of  the  sulphur  is 
favored  by  high  temperatures,  and  with  the  electric  furnace  the 
temperature  can  be  raised  to  any  desired  amount.  Smelting  in 
the  electric  furnace  can  also  be  carried  on  in  such  a  way  that, 
according  to  the  amount  of  reducing  material  used,  an  iron  can 
be  produced  of  any  desired  carbon  content,  even  practically  free 
from  carbon.  However,  it  is  a  question  whether  it  is  preferable 
to  produce  right  away  a  soft  material,  or  to  make  a  higher  carbon 
product  and  suitably  refine  this  later  by  special  processes.  Con- 
cerning this,  local  conditions  alone  can  lead  to  a  decision. 

In  smelting  lean  iron  ores,  more  electric  energy  is  required, 


334  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

because  the  impurities  have  to  be  heated  to  the  full  temperature 
of  the  charge,  and,  furthermore,  additional  flux  must  be  added 
to  slag  off  these  useless  impurities,,  and  the  extra  slag  must  also 
be  heated  to  the  temperature  of  the  furnace.  All  this  waste 
makes  the  process  correspondingly  more  expensive. 

Raw  spathic  ore,  brown  iron  ore,  etc.,  must  be  calcined  when 
smelted,  which  also  requires  electrical  energy  and  correspondingly 
increases  the  cost.  In  conclusion:  the  electric  production  of 
iron,  which  is  indeed  an  "infant  industry,"  must  be  accomplished 
without  the  loss  of  an  unnecessary  kilowatt  in  order  to  successfully 
compete  with  the  old  economically  working  blast  furnace. 

In  general,  therefore,  at  present  usually  high  percentage 
iron  ores,  preferably  magnetite  and  red  hematite,  are  smelted 
electrically.  If  it  happens  that  poorer  ores  have  to  be  used,  then 
they  must  be  previously  carefully  prepared  and  concentrated. 
During  this  concentration  it  is  well  to  remove  as  completely 
as  possible  any  pyrites,  apatite,  etc.,  which  may  be  present, 
and  thereby  help  in  the  production  of  a  highly  valuable  iron  of 
great  purity  similar  to  Swedish  or  Styrian,  which  will  be  suitable 
for  the  production  of  high  quality  steels.  The  fuel  must  also 
be  as  low  as  possible  in  ash,  so  that  the  slag  volume  is  not  in- 
creased too  much.  The  size  of  the  material  is  of  secondary 
importance  for  suitable  reduction,  but  very  fine  materials  are 
not  willingly  used  exclusively  because  of  the  difficulty  of  removing 
the  gases  produced  in  reduction. 

In  the  first  tests  carbon  and  ore  were  intimately  mixed, 
pressed  together  with  tar  and  used  in  the  form  of  briquettes. 
This  briquetting  is  unnecessary  and  can  be  more  readily  rejected 
as  it  is  costly,  for  in  those  countries  where  electric  smelting  is 
commercially  possible  because  of  dear  coke  the  price  of  tar  is 
also  correspondingly  high. 

Electric  smelting  of  iron  ore  can  be  carried  on  in  electric 
steel-making  furnaces.  The  mixture  for  reduction  will  either 
be  charged  altogether,  or  else  added  little  by  little,  depending 
on  the  type  of  furnace.  If  a  pool  of  liquid  pig  iron  has  formed 
on  the  hearth,  then  the  reduction  of  the  ore  mixture  will  progress 
more  quickly,  for  the  carbon  of  the  liquid  metal  takes  an  energetic 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  335 

part  in  the  reduction.  The  fluid  pig  iron  will  then  have  to 
be  recarburized  to  the  required  amount  by  the  carbon  of  the 
charge. 

In  regard  to  the  necessary  power  consumption,  that  type  of 
furnace  will  work  most  favorably  with  which  the  radiation  loss 
is  the  smallest. 

The  Stassano  furnace,  to  the  construction  of  which  the  first 
part  of  this  book  is  devoted,  heats  the  mixture  by  radiation,  for 
the  arcs  are  outside  of  the  material  to  be  heated.  But,  as  the 
arcs  radiate  heat  in  all  directions,  and  only  that  much  which 
radiates  downwards  is  used  economically,  it  is  to  be  expected 
that  the  efficiency  of  this  furnace  will  be  proportionately  low. 
On  the  other  hand,  the  electrode  consumption  will  not  be  very 
high  for  the  electrodes  are  not  in  contact  with  the  charge,  and  so 
will  not  be  attacked  by  the  iron  ore. 

i.  Smelting  of  Ore  in  the  Stassano  Furnace. — (The  charge 
heated  by  radiation  from  the  arc.)  Neumann  and  Goldschmidt 
have  published  results  of  the  following  smelting  test  (Staid  und 
Eisen,  1904,  pp.  687,  885).  The  analyses  of  the  materials  used 
were: 

Ore: 

FezO, 93-02%  P 056% 

MnO 62  CaO+MgO 5 

SiO2 3-79  H2O 1.72 

S 058 

Lime: 

CaO 51.21%  FezOj 50% 

MgO 3.11  SiO2 90 

A1203 50  C02 43-30 

Charcoal: 

Carbon 90.42%  Ash 3-88% 

Water 5.70 

Pitch: 

Carbon 59.20%  Hydrocarbons...    40.50% 

Ash 27 

Briquettes  were  made  from  a  mixture  of  1000  kg.  ore,  125  kg. 
lime,  1 60  kg.  charcoal,  120  kg.  pitch  (charcoal  and  pitch  together 


336    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

containing  230  kg.  carbon).  These  briquettes  constituted  the 
charge.  According  to  Stassano  the  heat  requirements  per  100 
kg.  ore  in  the  charge  are  calculated  as  follows,  the  data  below 
being  chosen  from  his  tables. 


Decomposition  of  the  oxide  of  iron      -     —  -  —  —  in  552.000 

Vaporizing  the  moisture  in  the  ore  and  charcoal 

(1.72  +1.21)637  =  1866.41 

Calcining  the  flux  12.5  X  425  ..............    =  5312.5 

Heating  the  CO,  to  500°  C.  542Q  X  '°l6  X  5^  =       987.09 

.044 

Heating  the  CO  produced  —   -  X  .0068  X  500  =  5921.667 

Melting  the  iron  produced  65  X  350  ..........  =  22775.2 

Melting  the  slag  produced  13.89  X  600  .......    =  8334.0 


157311.427 
Produced  from  the  burning  of  C  to  CO  20.9 

X  2175       45457.500 


Leaving 111853.927 

These  111,853.927  calories  correspond  to  129.386  kw.  hr. 
From  100  kg.  ore  65.114  kg.  of  iron  will  be  reduced,  so  that  the 
power  required  per  metric  ton  of  iron  is  1987.6  kw.  hrs.  This 
power  requirement  is,  however,  only  calculated  theoretically, 
and  figures  concerning  the  real  power  consumption  have  not 
been  published;  however,  as  shown  above,  the  radiation  loss 
with  the  Stassano  furnace  must  be  considerable. 

An  idea  of  the  amount  of  this  radiation  loss  is  obtained  from 
a  further  test  published  by  Goldschmidt  in  which  the  power 
consumption  is  given.  In  this  test  70.25  kg.  of  the  same 
briquettes  used  in  Test  No.  i  were  smelted  in  a  100  h.p.  furnace. 
The  output  was  30.8  kg.  iron  with  a  power  consumption  of  97.2 
kw.  hrs.  =  132.2  h.p.  hrs.  The  theoretical  power  consumption 
for  the  charge  may  be  calculated  on  the  basis  of  the  analyses 
given  above  as  follows: 


THE  ELECTRO-METALLURGY   OF  IRON  AND   STEEL  337 

For  the  reduction  of  the  iron  contained  in  the  final  product 
were  necessary  3  -  X  192   =  52730.262 

For  the  reduction  of  the  manganese  in  the  final 
product  were  necessary  — '^~  X  94.6    =        48.719 

For  melting  the  metal    30.8  X  350   =  10780.00 

For  melting  the  slag    6.3  X  600   =    3780.000 

For   heating    and     vaporizing     the    moisture 

1.316X637 =      838.292 

For  calcining  the  lime  6.25  X  475 =    2968.750 

For  superheating  the  steam  to  500°, 

1,316  X  400  X  .48  =      252.672 
For  superheating  the  CO2  to  500°  C, 

2.714  X  500  X  016 

=      493-554 

0.44 

For   superheating    the    hydrocarbons  to  500° 
2.43  X  500  X    .27 =     328.05 

For  superheating  the  CO  produced 

(3  X  30727  X3i2  +  28.336 
(  112  55 

X  500  X  .0068 =  2800.131 

Total  75020.330 

From  the  combustion  of  the  C  to  CO  were  produced 
9.883  X  2175 =  21495.525 

Leaving 53524.805 

As  the  whole  charge  consumed  97.2  kw.  hrs.  =  84012.072  cals., 
the  heat  efficiency  was: 

5,3524.805  X  ico  % 

84012.072 

The  power  consumed  per  metric  ton  of  iron  reduced  from  its 
ore  is  shown  to  be  3123  kw.  hrs.     Unfortunately  the  analysis 


338  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

of  the  metal  produced  is  not  given,  nor  the  length  of  time  of 
the  test.  The  demonstrated  efficiency  of  61.33%  ^s  n°t  very 
difficult  from  the  calculated  figure.  It  must  be  admitted 
that  not  only  was  this  a  test  melt,  but  that  several  of 
the  figures  calculated  gave  accidentally  very  favorable  results. 
In  operation  the  efficiency  would  undoubtedly  be  much  smaller, 
for  the  careful  supervision  possible  with  a  small  test  would  be 
lacking. 

Because  of  the  great  heat  radiation  in  the  furnace  which 
principally  attacks  the  roof,  the  life  of  the  roof  must  be  small, 
and  the  economical  carrying  on  of  the  process  depends  in  the 
first  place  on  the  durability  of  the  furnace.  In  order  to  make 
the  roof  somewhat  more  durable,  either  the  whole  or  at  least  that 
part  attacked  the  most  must  be  protected  by  water  cooling. 
This  water  cooling,  however,  apart  from  its  complexity  will  bring 
about  important  heat  losses,  the  amount  of  which  will  be  gone 
into  further  in  another  place. 

The  power  consumption  per  metric  ton  of  iron  is  seen  to  be 
high  as  was  to  be  expected.  Theoretically  it  is  1643  kw.  hrs.  or 
2680  with  a  furnace  efficiency  of  61.33%,  compared  with  a 
proved  figure  of  3123.  This  increase  in  practise  of  443  kw.  hrs. 
is  due  to  the  use  of  ore  which  is  not  theoretically  pure,  and  the 
consequent  melting  of  the  slag  produced,  the  burning  of  the 
lime,  vaporizing  the  water,  etc.,  a  proof  that  only  ores  as  pure 
as  possible  should  be  smelted.  With  the  smelting  of  more  im- 
pure ores  the  power  consumption  would  naturally  be  con- 
siderably higher  yet.  This  high  power  consumption  is  due  to 
the  great  radiation  loss  of  this  type  of  furnace,  and  can  therefore 
scarcely  be  lessened.  Further  disadvantages  are  that  no  con- 
tinuous operation  is  possible,  and  only  small  heats  can  be  pro- 
duced. From  this  it  is  evident  that  furnace  types  in  which, 
like  the  Stassano,  the  charge  is  only  heated  by  radiation  can  not 
be  considered  in  the  economical  smelting  of  ore. 

2.  Ore  Smelting  in  Electric  Hearth  Furnaces. — (Electrodes 
introduced  into  the  charge.) 

Theoretically  these  furnaces  should  work  well  because  the 
charge  so  nearly  surrounds  the  arc  that  the  heat  radiated  is 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  339 

completely  absorbed.  In  operation,  however,  such  a  total 
absorption  is  impossible,  the  charge  can  only  surround  the  arc 
to  a  limited  extent,  and  the  temperature  is  so  high  that  radiation 
through  the  charge  to  the  walls  of  the  furnace  is  unavoidable. 
With  such  furnaces  the  lining  and  the  special  roofs,  if  such  are 
present,  are  particularly  strongly  attacked  by  the  "stagnant 
heat,"  so  that  it  is  impossible  to  maintain  continuous  operation. 
Also  the  electrode  consumption  will  be  high,  for  the  electrodes 
are  in  contact  with  the  ore  mixture  and  will  be  attacked. 

Many  ore-smelting  tests  have  been  carried  out  with  different 
types  of  furnace  in  recent  years  in  order  to  remedy  the  trouble  re- 
sultant upon  the  attack  on  the  furnace  walls,  but  with  uncertain 
results.  In  every  case  the  power  consumption  has  been  much 
more  favorable  than  was  expected,  so  that  in  this  respect  the 
question  of  electric  smelting  of  ore  would  have  been  long  since  set- 
tled if  a  furnace  construction  had  been  found  more  suitable  for 
continuous  operation.  The  most  recent  tests  of  this  kind  have 
been  carried  out  by  Messrs.  Gronwall,  Lindblad  &  Stalhane, 
the  latest  test  furnace  being  shown  by  figs.  124,  125  and  126, 
invented  by  the  same  men.  One  metric  ton  of  white  iron  was 
produced  in  1909  with  0.25  h.p.  years  equals  2190  h.p.,  that  is 

"•  =  1622  kw.  hrs.,   a   result  that  closely  approaches  the 

theoretical  minimum,  and  is  to  be  explained  perhaps  by  the  very 
pure  ore  smelted.  Further  tests  made  with  the  Gronwall,  Lind- 
blad, Stalhane  furnace  are  given  elsewhere  in  Chapter  XIV,  under 
"Operating  Costs,"  and  under  B,  " Electro-metallurgy  of  Iron." 

THE    SMELTING    OF    ORE   IN    THE    INDUCTION    HEARTH 
FURNACE,  SYSTEM  ROCHLING-RODENHAUSER 

The  efficiency  of  this  furnace  will  not  be  bad  for  smelting 
ore,  notwithstanding  that  the  charge  is  only  heated  by  the  heat 
of  the  molten  bath,  because  the  bath  is  covered  with  cold  charge 
and  the  radiation  from  the  lower  part  of  the  furnace  can  be  kept 
low  by  means  of  suitable  brickwork,  etc. 

Above  everything  else,  however,  because  of  the  cooled  upper 
surface  of  the  bath  due  to  the  covering  of  the  charge,  and  the  heat- 


340  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

ing  from  within,  the  roof  will  show  great  durability,  which  is  a  very 
important  point,  if  there  is  to  be  continuous  operation.  Those 
furnaces  which  work  with  electrodes  and  have  a  roof  are  com- 
pelled to  use  extensive  water  cooling,  sometimes  in  order  to 
increase  the  life  of  the  furnace.  Through  the  avoidance  of  water 
cooling,  a  source  of  considerable  loss  of  heat  is  avoided,  so  that 
the  induction  furnace  is  worthy  of  serious  investigation  for  the 
smelting  of  ore. 

Many  smelting  tests  have  been  carried  out  in  the  Rochling- 
Rodenhauser  furnace,  and  some  reports  of  them  may  be  given, 
for  up  to  the  present  scarcely  any  results  of  ore  smelting  in  the 
induction  furnace  have  been  published.  High  sulphur  magnetite 
in  a  very  fine  state  of  division  was  used  and  high  sulphur  coke 
breeze,  in  order  to  produce  a  pig  iron  with  2.6  to  3.0%  carbon, 
and  as  low  in  sulphur  as  possible.  Although  it  was  assumed 
that  a  greater  part  of  the  sulphur  would  pass  away  as  gas  due  to 
the  following  reaction: 

FeS  +  2  FeO  =  3  Fe  +  S02, 

yet,  by  way  of  precaution,  the  theoretical  amount  of  lime  neces- 
sary to  combine  with  the  sulphur  as  sulphide  of  calcium  was 
added  to  the  charge,  together  with  that  necessary  for  the  acid 
gangue,  etc.  The  amount  of  slag  produced  in  this  way  was  not 
needlessly  increased,  although  the  CaS  produced  requires  a 
large  amount  of  slag  for  solution  if  it  is  hoped  to  produce  a 
sufficiently  good  desulphurization  in  this  way. 
Analysis  of  the  ore: 

Fe304  96-38%  =  69.79%  Fe  (          % 

FeS2  1.41      =    o.66%Fe^7045/0* 

Mn3O4  0.25      =    o.i8%Mn. 

Si02  0.60 

P2O,  0.05      =    0.02%  P. 

CaO  o.io 

MgO  i. 21 

100.00 

Oxygen  combined  with  Fe  &  P  =  26.62%. 
Total  sulphur  in  the  ore  =  0.75%. 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  341 

ANALYSIS  OF  THE  COKE  BREEZE 

Carbon 87 . 48% 

Sulphur i  .068% 

Ash 10.4% 

The  principal  constituents  of  the  coke  ash  were: 

SiO2 40.6  % 

CaO 5.6% 

Fe ii. 6  % 

A12O3 25.40% 

Oxygen  combined  with  iron  =  5.0%. 
The  carbon-monoxide  produced  passes  away  unused. 
Chemical  Balance  Sheet.— 100   kg.  ore    (i/io  of    a  metric 
ton)  =  70.45  kg.  iron.     This  requires: 

(a)  For  reduction  and  combination  of  the  26.62  kg.  oxygen, 

C  +  0  =  CO 
i60  +  12  C  =  28  CO 
26.62  X  12 


16 


19.97  kg- 


26.62  X  28  0 ,      ~~ 

and  produce =  46.58  kg.  CO 

(b)  70.45  kg.  Fe  carburized  to  3%  require 

?°^JO  =  2tl8k     c 
97 

(c)  0.75  kg.  S  combined  with  CaO  to  form  CaS  require: 

S  +  CaO  +  C  =  CaS  +  CO 

32  +  56  +  12    =   72  +  28 

0.75  kg.  S  +  1.28  kg.  CaO  +  0.28  kg.  C 
=  1.70  kg.  CaS  +  0.70  kg.  CO 

The  total  amount  of  carbon  is  therefore  19.97  +  2.18  -f  0.28 

=  22.43 

corresponding  to  22-43  X  100  =  ^^  kg  coke  breeze> 
57.45 


342    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

As,  however,  the  ash  of  the  coke  also  requires  a  small  amount  of 
carbon  for  the  reduction  of  its  metallic  oxides,  the  calculations 
should  be  made  with  25.80  kg.  of  coke  breeze.  This  25.80  coke 
breeze  contains  0.258  X  1.068  =  0.28  kg.  sulphur  which  must 
be  slagged  off  as  CaS. 

0.28  kg.  S  +  0.49  kg.  CaO  +  o.io  kg.  C  =  0.63  kg.  CaS  + 
0.24  kg.  CO. 

25.80  kg.  coke  breeze  contains 

10.4  X  116  X  25.8 
—  -  -  2-  =  0.31  kg.  Fe, 

10000 

and 

10.4  X  5  X  25.8  ^     ,          .      .  , 

-  "  --  =  0.13  kg.  O,  in  the  form  of  oxide  of  iron. 

16  0  +  12  C  =  28  CO  or 
0.13  O  +  o.io  C  =  0.23  CO 
100  kg.  ore  therefore  require 
22.43  +  °-10  +  °'10  —  22.63  kg.  carbon  or 

-    =  25.87  kg.  (57.03  Ibs.)  coke  breeze. 


THEORETICAL  AMOUNT  OF  SLAG  PER  100  KG.  ORE  SMELTED 
From  the  ore  From  the  coke  ash 

0.2587  X  10.4  =  2.69  kg. 
SiO2      0.60  kg.  SiO2    i.  09  kg. 

CaO      o.io  kg.  CaO    0.15  kg. 

MgO     1.2  1  kg.  A12O3  0.69  kg. 

1.91  kg.  2.69  kg. 

from  this  must  be  taken  0.166  X  10.4  X  0.2587  =  0.44  kg.  Fe3  04, 
leaving  2.69  —  0.44  =  2.25  kg.  slag. 

CaS  produced  1.70  +  0.63  =  2.33  kg. 

Lime  addition  for  combining  with  the  sulphur  1.28  +  0.49  =  1.77 
Lime  addition  for  slag  ...................................  1.41 

Total  lime  addition  ...............................  3.18 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  343 

The  theoretical  total  amount  of  slag  is  1.91  +  2.25  -f  2.33  + 
3.18  =  9.67. 

In  calculating  the  amount  of  carbon  necessary  for  reduction, 
it  must  be  remembered  that  before  the  beginning  of  the  test 
the  furnace  was  filled  with  1000  kg.  of  refined  Basic  Bessemer 
metal,  which  latter  had  to  be  recarburized  to  the  required 
amount.  After  this  the  following  mixture  was  charged: 

597.5  kg.  ore  +  183.5  kg-  coke  breeze  +  19.0  kg.  lime  =  800  kg., 

compared  with  the  theoretical  amount  which  does  not  consider 
the  recarburization  of  the  refined  Bessemer  metal: 

597.5  kg.  ore  +  154.6  kg.  coke  breeze  +  19.0  kg.  lime. 

The  Bessemer  metal  had  a  temperature  of  1650°  C.  The  ore 
was  charged  as  uniformly  as  possible,  and  in  comparatively  large 
amounts.  Care  was  taken  that  the  bath  was  always  covered 
with  the  mixture  in  order  to  keep  the  radiation  loss  as  low  as 
possible;  a  method  of  working  that,  in  general,  was  not  hard  to 
maintain. 

The  slag  produced  during  the  tests  was  only  removed  once, 
and  the  exact  amount  was  obtained.  As  the  furnace  used  for 
the  tests  was  mounted  on  a  scale,  the  weight  of  the  Bessemer 
metal  charged  and  the  finished  material  were  also  obtained 
exactly.  The  smelting  of  the  800  kg.  of  charge  required 
1030  kw.  hrs. 

SMELTING  RESULT 

(a)  Output  of  Slag. 

99  kg.  slag  with  9.12%  FeO  =  7.09%  Fe  and  2.60%  S. 
Theoretically  the  slag  should  contain: 

1.  From  the  charge  9.67  X  5.975  =  57-78  kg--  -57-78  kS-  slaS- 

2.  Lime  for  slagging  (3.18  —  1.77)  =  (1.41  X 

5-975)  = 8.42kg.slag. 

3.  Excess  of  coke  breeze  = 3-°°  kg-  slag- 

4.  Slag  remaining   in    furnace  from  previous 

heat  = •- '•  •  •  •  20.8  kg.  slag. 

Weight  of  slag  = 90.00  kg.  slag. 


344    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  weight  of  this  slag  is  increased  by  its  iron  contents 

90  X  100 

-  -  =  oo  kg.  which  contains 
100  -  9.12 

X  QQ  , 

7.02  kg.  iron. 


IOO 

(b)  Output  of  Iron. 

looo  kg.  of  Basic  Bessemer  was  charged  containing: 

C.  06%  P.  093%  S.  073%, 

1427  kg.  electric  pig  iron  were  tapped  with  2.64%  C,  0.02%  Si, 
°-°73%  P>  0.076%  S,  of  which  1427  —  1000  =  427  kg.  were 
produced  from  the  mixture.  The  theoretical  amount  is  — 

(1)  From  the  ore  5.975  X  0.7045  =  420.94 

(2)  From  the  coke  ash, 

•1.835  X  n.  6  X  10.4  2.20 

—  =  kg.  iron  =  - 
loo  423-14 

From  this  kg.  iron  =  —  ^—  went  to  the  slag. 
416.12 

This  weight  when  calculated  to  electric  pig  iron  equals 
416.12 


0.9736 


427  kg. 


The  loss  of  metal  in  the  slag  is  therefore-^— =  1.6%. 

4.2314 

CHEMICAL  BALANCE 

(a)  The  Carbon. 

1,000  kg.  Basic  Bessemer  metal  with  0.06%  C.  carbur- 

ized  to  2.64%  C.  require  (2.64  —  .06)  1,000  =  . . .  25.8  kg.  C. 

427  kg.  electric  pig  iron  contain  427  —  416.12  = IO.88  " 

The  reduction  process  requires  5.975  X  19-97  = 119.32  " 

The  formation  of  CaS  requires  (0.28  +  o.io)  5.975  =..  2.27  "    " 
The  reduction  of  the  iron  oxide  in  the  coke  ash  requires 

0.10X5.975= 0.98  "" 


159.25  kg.  C. 

As  87.48  kg.  C  =  loo  kg.  coke  breeze,  this  159.25  kg.  C 
182.0  kg.  coke  breeze. 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  345 

(b)  The  Sulphur. 
Brought  in: 

597-5  kg.  ore  at  0.75%  S  = 4. 48  kg.  S 

l83  •  5  kg.  coke  breeze  at  1 .068  S  = i  .96    " 

20 . 8  kg.  slag  held  back  containing  i.o%S  =  ...     0.21     " 

6.65kg.  S 

Taken  out: 

99      kg.  slag  at  2.6%  S  = 2.57kg.  S 

427      kg.  electric  pig  iron  at  0.076%  S= 0.32    " 

2. 89  kg.  S 

Therefore   6.65  -  2.89  =  3.76   kg.  S  or   56%   of   the  total 
sulphur  was  gasified. 

(c)  Phosphorus. 

1000     kg.  Basic  Bessemer  metal  at  0.093%  P  = o .  93  kg.  P 

597-5  kg.  ore  at  0.02%  P  = 0.12       " 

P  brought  in 1 .05  kg.  P 

1427  kg.  electric  pig  iron  at  0.073  need  = 1 .05  kg.  P 

(d)  The  Furnace  Gases. 

12  C  +  i6O  =  28  CO 
Therefore  (119.32  +  2.27  +  0.98)  = 

122.57  kg.  C  +  163.43  kg.  O  =   286.0    kg.  CO 
183.5—  182.0  =  1.5  excess  coke  cor- 
responds to   1.31   C.     This  was 
charged  in  excess,  burned  with 

air  gives 3.05  kg.  CO 

The  burning  takes  place  with  1.74  kg. 

O,  that  bring  in 6.54  kg.  CO 


The  total  gas  made  is  295. 59  kg. 
HEAT  BALANCE 

The  furnace  was  held  at  1300°  C.  during  the  test,  and  the 
iron  tapped  at  the  same  temperature.  The  mixture  for  reduction, 
therefore,  had  to  be  first  heated  to  this  temperature  after  charg- 
ing. 


346  ELECTRIC  FURNACES  IN  THE   IRON  AND  STEEL  INDUSTRY 

1.  Heat  Expended. 

1.  597-5  kg.  ore  require  597.5X1300X0.20= 155,350  cals. 

2.  183.5  kg.  graphite,  183.5X1300X0.23  = 48,426     ' 

3.  19.0  kg.  lime  require  19X1300X0.21  = 5,187     " 

4.  416.12  kg.  iron  reduced  from  FesO4  require  1648 

X4I6.I2  = 685,765     " 

5.  5,975X0.02  kg.  P  to  be  reduced  from  P2O5  re- 

quire 0.12X5966= 716     ' 

6.  427  kg.  pig  iron  require  for  melting  427  X46  =  . .      19,642     ' 

7.  90—20.8=69.2  kg.  slag  require  for  melting  69.2 

X30  = 2,076     " 

8.  2.89kg.  S  changed  into  CaS  require  2.89X1093=      3,159     " 

920,321  cals. 

2.  Heat  Brought  in. 

1,000  kg.  Basic  Bessemer  metal  cooled  from  1650° 

to  1300°  bring  in  1000X350X0.2  = 70,000  cals. 

Burning  3.76  kg.  S  to  SO2  = 8,347     " 

183.5  kg.  coke  breeze  =  160.53  kg.  C.  For  carbur- 
izing  the  pig  iron  26.40+10.88  =  37.28  required. 
The  remainder,  123.25  kg.  burned  to  CO  bring 
in  123.25X2473= 304,797  " 

1030  kw.  hrs.  used  in  the  test  1030X864.5  = 890,435     " 


Heat  brought  in  = 1,273,579  cals. 

Therefore  the  efficiency  of  the  furnace  equals 
920321  X  100 

I273579 

In  determining  the  energy  necessary  to  produce  i  metric  ten 
pig  iron  it  must  be  remembered  that  the  basic  Bessemer  metal 

charged  at  1650°  brings  in  ~ —  =  81  kw.  hrs.,  for  the  finished 

material  was  tapped  at  1300°  C.    Therefore  1030  +  81  =  mi 
kw.  hrs.  were  required  to  produce  427  kg.  electric  pig  iron,  which 

equals  for  the  metric  ton =  2602  kw.  hrs. 

427 

The  following  important  points  were  established  by  means 
of  the  test. 

(i)  The  efficiency  of  the  furnace  is  good,  as  was  to  be  expect- 
ed. It  may  be  still  further  increased  if  the  mixture  for  reduction 
were  charged  by  machinery  and  not  by  hand,  so  that  the  frequent 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL          347 

opening  of  the  working  doors  and  the  unavoidable  heat  losses 
could  be  avoided. 

(2)  The  reduction  of  the  ore  takes  place  satisfactorily  even 
with  the  use  of  dense  fuel,  chemically  inactive,  such  as  coke 
breeze  with  a  high  content  of  ash.    The  amount  of  reduction 
material  necessary  closely  approaches  the  theoretical,  due  to  the 
reducing  atmosphere  of  the  electric  furnace. 

(3)  The  phosphorus  in  the  charge  goes  entirely  into  the  iron. 

(4)  The  sulphur  in  the  charge  is  lowered  more  than  half,  due 
to  the  reactions  between  the  oxides  and  sulphides  of  iron,  so  that 
lime  additions  to  unite  with  the  sulphur  are  probably  unneces- 
sary. 

Test  2. — In  order  to  increase  the  efficiency  of  the  furnace  ef- 
forts were  made  to  lower  the  radiation  from  the  upper  surface  of 
the  bath  by  causing  the  charge  to  project  still  deeper  into  the  iron 
bath  in  the  hearth.  A  suitable  way  appeared  to  be  the  smelting 
of  the  charge  in  the  form  of  briquettes.  The  -briquettes  were 
made  of  the  same  mixture  as  used  in  Test  No.  i  plus  8%  of  steel- 
works tar.  The  whole  was  ground  in  a  Chili  mill,  and  pressed 
in  an  ordinary  dolomite  press.  The  briquettes  were  burned  a 
little  before  being  used.  An  interesting  point  is  that  these 
partially  burned  briquettes  showed  0.35%  reduced  metallic  iron. 

A  lowering  in  the  power  consumption  with  the  use  of  these 
briquettes  could  not  be  proved,  nor  any  increased  smelting 
efficiency  of  the  furnace  compared  with  Test  No.  i.  The  pig 
iron  produced  had  a  low  sulphur  content,  and  the  chemical 
balance  showed  that  a  greater  part  had  been  gasified  as  S02. 
The  same  amount  of  ore  was  smelted  as  in  Test  No.  i. 

Test  3. — As  both  tests  showed  that  over  half  the  total  sulphur 
was  gasified,  and  the  iron  was  sufficiently  low  in  sulphur,  further 
tests  were  made  on  a  mixture  of  ore  and  fuel  without  special  lime 
additions.  It  was  thought  that  because  of  the  smaller  slag 
volume,  the  power  consumption  would  be  lower,  and  that  at  the 
same  time  the  iron  would  be  sufficiently  low  in  sulphur. 

After  Test  2  had  shown  the  lack  of  efficiency  of  briquetting, 
the  ore  was  used  fine  as  it  was  taken  from  concentrating,  and  the 
coke  breeze  of  the  usual  size.  The  results  of  the  test  were  good. 


348  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

A  low  sulphur  white  iron  was  produced,  and  somewhat  fewer 
kw.  hrs.  per  metric  ton  were  necessary  than  with  Test  i,  and  the 
furnace  efficiency  was  somewhat  higher;  that  is,  the  smelting 
time  was  somewhat  shorter  than  with  Tests  i  and  2. 

Test  4. — This  test  was  to  show  whether  an  addition  of 
granulated  iron  to  the  mixture  would  shorten  the  time  of  melting, 
and  give  a  saving  in  the  energy  consumed.  It  was  really  a 
carrying  out  of  the  so-called  Lash  process,  which  consists  of 
using  a  mixture  of  ore,  carbon,  and  slag-producing  material  with 
finely  divided  pig  iron,  the  charge  being  kept  loose  and  porous 
with  sawdust.  The  reduction  of  the  ore  is  helped  by  the  carbide 
present  in  the  pig  iron.  An  example  of  a  Lash  mixture  is  as 
follows : 

Iron  ore 54% 

Cast-iron  t  urnings  or  granulated  cast-iron 27 

Sawdust 4 

Limestone 4 

Tar 3 

Coke...  8 


100% 

From  what  has  been  said  before,  it  is  to  be  expected  that 
ore  reduction  by  the  Lash  process  would  give  no  advantage,  for 
in  the  induction  furnace  there  is  present  a  permanent  bath  of 
metal,  and  therefore  with  the  ordinary  ore  mixture  the  known 
good  reactions  in  the  Lash  process  must  take  place  anyway.  In 
melting  a  metric  ton  of  pig  iron  by  the  Lash  process,  the  power 
consumption  will  be  rather  bad  because  the  iron  enclosed  in  the 
charge  has  to  be  melted  electrically. 

The  reduction  mixture  was  charged  in  exactly  the  same  way 
as  described  by  Lash.  The  result  of  the  test,  however,  gave 
neither  a  shorter  melting  time  nor  a  lower  power  consumption 
per  metric  ton  of  pig  iron  from  ore. 


THE   ELECTRO-METALLURGY   OF  IRON  AND   STEEL  349 

CRITICISM  OF  IRON  ORE  SMELTING  IN  THE  ELECTRIC  HEARTH 
FURNACE 

The  smelting  of  iron  ore  in  the  electric  hearth  furnace,  which 
is  so  simple  experimentally,  depends  on  two  important  factors 
before  it  can  be  carried  out  commercially.  One  of  them  is  the 
power  consumption,  the  other  the  durability  of  the  furnace  lining, 
that  is,  the  costs  for  repairs  per  metric  ton  of  iron  produced. 

The  durability  of  the  lining  requires  that  the  highest  tem- 
peratures, such  as  those  of  the  arc,  must  be  avoided  because  the 
drop  in  temperature  is  too  great  for  it  to  be  taken  up  by  the 
charge. 

This  question  of  smelting  ore  in  the  electric  hearth  furnace  is 
therefore  only  to  be  solved  by  a  type  of  furnace  that  does  not 
work  continuously  at  the  highest  temperatures,  and  with  which 
the  excess  heat  which  attacks  the  lining  can  be  carried  off.  In 
this  case  the  lining  costs  will  be  very  small,  but  a  somewhat 
higher  power  consumption  must  be  counted  on. 

From  the  discussion  above  the  only  furnace  of  this  type  at 
present  is  the  induction  furnace,  and  the  tests  show  that  on  the 
one  hand  the  furnace  lining  allows  continuous  operation,  and  on 
the  other  that  the  power  consumption  is  within  such  limits  that, 
under  certain  conditions,  successful  competition  with  the  blast 
furnace  is  permissible.  Such  conditions  are  first,  that  there  are 
no  special  requirements  in  regard  to  the  physical  properties  of 
the  ore  and  fuel.  Even  very  fine  raw  materials  can  be  smelted, 
but  the  best  are  of  small  grain  size. 

This  factor  becomes  more  important  from  day  to  day,  for 
conditions  continually  press  towards  the  mining  of  poorer  grade 
ores  and  magnetic  concentration,  so  that  high  percentage 
concentrates,  small  in  size,  are  coming  on  the  market.  If  these 
concentrates  are  to  be  smelted  in  the  blast  furnace,  they  must  be 
first  agglomerated  or  briquetted,  a  process  that  even  without  a 
binding  agent,  that  is,  using  high  pressure  alone,  or  say  sinter- 
ing, is  an  additional  expense,  for  in  this  case  a  preroasting 
cannot  be  avoided. 

Also  in  smelting  ore  in  the  electric  hearth  furnace  a  small 


350  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

sized  material  can  be  used  for  reduction  with  at  least  equal 
success  to  one  of  moderate  size,  which  means  that  small  waste 
fuel  of  any  kind  is  available  that  up  to  now  has  been  valueless. 
Even  these  two  points  are  so  important  that  under  certain  con- 
ditions they  will  allow  the  electric  hearth  furnace  to  work  more 
economically  than  the  blast  furnace.  Also  in  regard  to  the 
purity  of  the  ores,  especially  the  sulphur,  the  electric  hearth 
furnace  has  great  possibilities  because  of  the  considerable 
volatilization  that  takes  place.  High  sulphur  materials  can  be 
smelted,  therefore,  with  acid  slags  and  without  the  lime  additions 
that  are  absolutely  necessary  in  the  blast  furnace.  Only  so 
much  basic  flux  need  be  charged  as  is  necessary  to  give  a 
liquid  slag. 

The  concentration  of  the  ores  will  therefore  not  have  to  be 
carried  so  far,  especially  when  ores  with  an  acid  and  basic  gangue 
are  to  be  used  at  the  same  time,  for  by  suitable  mixing  a  self- 
fluxing  charge  can  be  obtained.  This  allows  the  conclusion  to  be 
drawn,  that  under  certain  conditions  the  poorer  iron  ores  can  be 
smelted  in  the  electric  hearth  furnace  without  previous  prepara- 
tion, especially  if  the  gangue  forms  a  flux,  so  that  the  iron  output 
of  the  charge  is  not  lowered  by  the  addition  of  fluxes. 

A  further  important  advantage  of  smelting  ore  in  the  electric 
hearth  furnace  is  that  the  harder  steels  can  be  produced  direct. 
It  is  not  favorable  to  immediately  make  a  soft  steel,  for  the  iron 
bath  is  first  carburized  by  the  reducing  material,  so  that  at  the 
end  of  the  heat  ore  alone  must  be  added  in  order  to  remove  this 
carbon. 

In  the  next  section  of  the  book  it  is  explained  how  this  process 
is  comparatively  expensive.  Still  steel  with  about  1.5  to  1.8% 
carbon  can  be  produced  direct,  and  if  high  in  sulphur  can  be 
desulphurized  at  little  cost;  while,  at  the  same  time,  if  high  in 
phosphorus  it  can  be  dephosphorized  without  removing  the 
carbon,  both  by  means  of  processes  given  in  more  detail  in  the 
next  chapter. 

The  carbon  consumption  in  the  electric  hearth  furnace  is  as 
good  as  possible  when  the  carbon  is  only  burned  to  carbon-mon- 
oxide. Troubles  that  are  always  more  or  less  unavoidable  in 


THE  ELECTRO-METALLURGY  OF   IRON  AND  STEEL  351 

the  blast  furnace  disappear  altogether,  as  also  the  production  of 
the  valueless  "transition  iron,"  when  the  furnace  is  changed 
from  one  kind  of  iron  to  another.  Add  to  this  the  simpler 
operation,  the  avoidance  of  water  cooling,  the  possibility  of  reg- 
ulating at  will  the  temperature  of  the  metal  tapped,  and  no 
electrode  consumption,  are  some  of  the  results.  All  these  are 
points  that,  under  certain  conditions,  allow  the  electric  hearth 
furnace  to  successfully  compete  with  the  shaft  furnace  for  smelt- 
ing ore. 

THE  SMELTING  OF  IRON  ORES  IN  THE  ELECTRIC  SHAFT 
FURNACE 

The  experiments  made  in  the  electric  hearth  furnace  make 
one  desirous  of  studying  more  economical  methods  of  smelt- 
ing. The  disadvantages  of  the  electric  hearth  furnace  are 
briefly: 

1.  Low  melting  efficiency  of  the  furnace  during  operation. 

2.  Large  power  consumption  per  ton  of  iron  produced. 

3.  Frequently  too  high  a  consumption  of  reducing  material. 
The  reason  for  the  low  furnace  efficiency  is  that  the  mixture 

for  reduction  is  charged  cold  so  that  it  has  to  be  heated  electrically 
to  the  necessary  temperature.  As  the  radiation  loss  increases 
with  the  smelting  time  per  ton,  it  follows  that  a  shortening  of 
the  smelting  time  would  give  a  better  efficiency,  and  this  requires 
the  charging  of  heated  material.  This  preheating  must  naturally 
be  brought  about  without  increased  consumption  of  electric  or 
other  energy  if  possible,  and  the  hot  waste  reduction  gases  are 
available  without  extra  cost.  They  are  most  suitably  used  by 
charging  the  mixture  high  in  the  furnace  so  that  the  gases  have 
to  pass  through  it,  giving  up  their  heat.  This  necessitates 
arranging  a  shaft  on  the  hearth  furnace. 

The  carbon-monoxide  produced  in  the  hearth  would  not  only 
have  a  thermal  effect  but  also  a  chemical  one,  that  is,  the  ore 
would  be  partly  reduced,  so  that  the  furnace  then  has  only  to 
melt  the  iron  in  the  mixture  of  iron  and  ore.  In  other  words 
only  the  remainder  of  the  iron  ore  has  to  be  reduced,  and  the 
furnace  is  released  from  some  of  its  work. 


352   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

If  the  reduction  gases  are  used  only  to  preheat  the  charge, 
then  the  following  rough  calculation  gives  the  advantage  obtained: 
533  cu.  m.  (1880  cu.  ft.)  of  gases  are  produced  per  metric  ton  of 
iron,  and  the  same  may  be  used  for  preheating  the  charge  and 
be  cooled  down  to  200°  C.  There  will  be  obtained  therefore: 

533  X  1 100  X  0.24  =  140712  cals.,  corresponding  to  = 

004.5 

162.8  kw.  hrs.  In  producing  a  pig  iron  with  3%  carbon  there 
would  be  a  saving  in  energy  of  — =  10.14%,  which  means 

that  the  metric  ton  of  pig  iron  will  be  smelted  with  1605.5  ~~ 
162.8  =  1422.7  kw.  hrs. 

On  the  other  hand  if  the  waste  gases  are  used  only  for  pre- 
liminary reduction  of  the  ore,  then  the  following  rough  calculations 
are  obtained  for  the  limiting  case  that  the  CO  is  all  changed  to 
CO2.  According  to  the  equation  Fe304  +  2  C  =  Fe3  +  2  C02 
the  metric  ton  of  iron  would  only  require  143  kg.  of  carbon  for 
reduction.  Also,  according  to  the  equations: 

Fe3O4  +  4C     =  3  Fe  +  4  CO 
Fe3O4  +  4  CO  =  3  Fe  +  4  CO2 

i      94IOQ  +  45°oo 
only  -  —  =  493000  cals. 

would  be  necessary.  The  total  carbon  required  for  the  produc- 
tion of  a  3%  carbon  pig  iron  will  be  143  +30  =  173  kg.  for 
1030  kg.  metal,  and  the  following  heat  balance  is  obtained  for 
this  most  favorable  case. 

1383   kg.   ore   heated  to    1300°   C.  =  1381X0.2 

Xisoo =359,060  cals. 

173  kg.  C.  heated  to  1300°  C.  =  173X0.2X1300  =   44,980     " 

1000  kg.  iron  heated  to  reducing  temperature ..  =493,000     " 

looo  kg.  iron  heated  to  melting  temperature.  . .  =  47,880     " 


944,920  cals. 

This  corresponds  to  —      —  =  1093  kw.  hrs.  per  1030  kg.  pig 
864.5 

iron,  or  1061  kw.  hrs.  per  metric  ton.     It  is  here  assumed  that 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  353 

the  CO2  leaves  the  furnace  at  1300°  C.,  and  if  the  excess  heat 
of  the  CO2  were  further  used  to  preheat  the  charge,  and  the  gas 
allowed  to  escape  at  200°  C.,  then  the  power  required  would  be 
lowered  as  follows: 

From  the  equation  Fe3O4  +  2  C  =  Fe3  +  2  C02 
168  kg.  Fe  produce  2  X  22.4  =  44.8  cu.  m.  CO2,  or  268  cu.  m. 
per  metric  ton  of  iron.     If  the  heat  from  1300°  to  200°  is  used 
for  preheating  then  there  is  obtained  268  X  0.24  X  noo  =  70752 

cals.,  corresponding  to  ^p^  =  81.8  kw.  hrs.     In  this  case, 

therefore,  1061  —  81.8  =  979.2  kw.  hrs.  are  necessary  to  pro- 
duce i  metric  ton  of  pig  iron. 

From  this  it  may  be  seen  that  the  use  of  the  furnace  gases 
for  reducing  the  ore  brings  about  a  considerable  lowering  in  the 
power  required,  just  as  well  as  their  use  for  preheating  alone. 
By  utilizing  these  gases  as  much  as  possible,  the  electric  furnace 
is  relieved  a  great  deal  and  the  smelting  time  is  considerably 
shortened.  The  idea  of  using  the  reduction  gases  is  therefore 
justified  particularly  as,  at  the  same  time,  there  is  obtained 
a  desirable  and  much  lower  consumption  of  reducing 
material. 

As  is  well  known,  however,  carbon-monoxide  can  only 
be  used  up  to  a  certain  limited  amount  for  the  reduction 
of  ore  because  the  mixture  of  CO  and  CO2  produced  has  no 
more  reducing  influence  when  a  certain  percentage  of  CO2 
is  present.  In  the  electric  shaft  furnace,  therefore,  .one  has 
to  figure  on  a  waste  gas  that  consists  largely  of  CO, 
and  it  is  apparent  that  the  carbon  necessary  for  reduction 
will  increase  with  increasing  percentage  of  CO  in  the  waste 
gases. 

In  smelting  magnetite  the  carbon  necessary  per  metric  ton 
of  pig  iron  with  3%  carbon,  when  the  percentage  by  volume  of 
C02  in  the  waste  gases  is  known,  is  calculated  by  the  formula 

286  (ICQ  -  3)  +  3° 
100  +  CO2% 

In  this  way  the  following  table  has  been  prepared: 


354    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


Per  cent.  CO2  in 
waste  gases 

IOO 

Kg.  carbon  required  per 
metric  ton  pig  iron  of 
3%C. 

T-lS 

90 

14.6 

80 

154. 

70              .    . 

161 

60  

17^ 

50  

184 

40  

198 

v> 

20    . 

2'W 

10   

2*2 

0.  . 

277 

The  principle  of  an  addition  of  a  shaft  is  naturally  possible 
with  any  electric  hearth  furnace  that  has  a  fairly  large  hearth, 
and  is  the  easiest  in  the  case  of  the  arc  furnaces,  for  these  always 
have  a  comparatively  large  hearth.  The  Stassano  furnace  forms 
an  exception,  for  here  the  charge  is  heated  by  radiation  alone  and 
only  the  heat  below  the  arc  is  used.  Also  the  induction  furnace 
can  be  built  so  that  it  is  easy  to  add  a  shaft,  and  further  as  the 
depth  of  bath  in  the  induction  furnace  can  be  fixed  at  any 
desired  amount  a  shaft  about  3  m.  (10  ft.)  high  or  over  is  per- 
missible, which  is  completely  sufficient  because  of  the  small 
amount  of  reduction  gases  produced  and  their  slow  passage 
through  the  shaft. 

In  principle,  reduction  with  gaseous  fuel  is  always  preferable 
to  solid  fuel,  for  the  latter  only  reduces  the  outer  layers  of  the 
ore.  Because  of  this  the  use  of  a  gaseous  reducing  agent  should 
shorten  the  time  of  operation  and  increase  the  efficiency  of  the 
furnace,  for  the  reasons  already  given.  At  first  it  was  feared 
that,  with  the  use  of  a  shaft,  the  heat  would  be  immediately 
carried  upward  from  the  metal  bath  and  the  operation  of  the 
furnace  thereby  made  more  difficult.  These  fears,  however, 
were  shown  to  be  groundless  because  preheating  helped  the 
furnace  so  that  the  same  condition  was  obtained  as  before,  but 
in  a  shorter  time.  It  will  be  shown  that  the  carrying  away  of 
heat  from  the  hearth  to  the  shaft  only  takes  place  slowly,  and 
that  in  arc  furnaces  the  heat  must  be  artificially  removed  from 
the  lower  part  of  the  furnace. 


THE    ELECTRO-METALLURGY   OF  IRON  AND   STEEL 


355 


In  addition  to  the  economic  advantages  of  the  electric  shaft 
furnace  compared  with  the  hearth  furnace,  the  disadvantages 
should  not  be  overlooked.  They  are: 

1 .  No  very  fine  material  can  be  smelted,  but  only  pieces  that 
are  not  too  large,  nor  on  the  other  hand  ore  smaller  than  a  hazel- 
nut. 

2.  In  smelting  there  is  no  removal  of  sulphur,  therefore  with 
ores,  etc.,  rich  in  sulphur  there  must  be  added  the  necessary 
amount  of  fluxes  to  slag  off  the  sulphur. 

3.  The  slag  must  be  tapped  as  a  thin  liquid,  so  that  for  this 
reason  fluxes  also  must  be  added,  which  decreases  the  output 
from  the  charge.     Therefore  at  present   only  high  percentage 
ores  can  be  used. 

4.  Only  iron  with  considerable  carbon  can  be  produced,  not 
the  high  carbon  steels,  and  the 

subsequent  refining  of  the  iron  is 
expensive. 

5.  The    electrodes    must    be 
burdened   only   up   to  a  certain 
amount  per  sq.  cm.  of  section,  so 
that  with  coke  alone  the  voltage 
must  be  lowered,  and  with  it  the 
furnace  efficiency. 

The  first  important  experi- 
ments with  an  electric  shaft 
furnace  were  carried  out  by 
Heroult. 

SMELTING  TESTS  IN  THE  SPECIAL 
HEROULT  FURNACE 

These  very  extensive  experi 
ments  were  carried  out  at  the 
request  of  the  Canadian  Govern- 
ment in  1906  at  Sault  St.  Marie, 
Ontario,  in  a  furnace  built  by 
Heroult.  As  the  accompanying 
illustration  shows,  Fig..  123,  the  FIG.  123 


35G  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

furnace  differs  very  much  from  the  Heroult  steel  furnace,  and 
approaches  the  Girod  in  principle.  The  lower  part  is  formed  of 
carbon  material  stamped  into  place  and  constitutes  one 
electrode,  while  the  other,  1.8  m.  (72  inches)  long,  reaches  into 
the  shaft  from  above  and  can  be  raised  and  lowered.  The 
shaft  is  1115  mm.  fo'-io")  high.  It  is  slightly  conical  and  'is 
built  of  fire-brick.  The  current  was  delivered  to  the  furnace 
at  50  volts  pressure. 

Below  are  given  details  of  these  tests  which  are  of  the  greatest 
interest  because  the  electrode  and  furnace  lining  stood  up  for 
at  least  several  days. 

Test  No.  13. — The  raw  materials  had  the  following  compo- 
sition: 

Wilbur  Magnetite, 


SiO2      = 

6.20% 

Fe203    = 
FeO      = 

£^-56.69% 

A120,    = 

2.56% 

CaO     = 

2.00% 

MgO    = 

6.84% 

MnO    = 

0.258% 

PA      = 

0.023% 

P=O.OI% 

S 

0.05% 

CO,      = 

3-609% 

100.00% 

Charcoal, 

Moisture        .  =   14.00% 
Volatile  matter  =   27.56% 

Fixed  carbon  =   55.90% 

Ash  =     2 . 54% 

S  =     0.058% 

Sand, 

SiOz  =81.71% 

Fe2Oj  =  0.09% 

A12O3  =14-27% 

CaO  =    i.  60% 

MgO  =   1.11% 

Alkali  =    1.22% 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL          357 

The  test  lasted  61  hrs.,  25  mins.    The  results  were: 

9573  •  23  kgs.  ore  smelted 
2973-75     "    charcoal  smelted 

540.23     "    sand  smelted 
5832.  '     pig  iron  produced 

462.67     "     charcoal  used  per  metric  ton 
1726        kw.  hrs.  used  per  metric  ton 

The  analyses  of  the  pig  iron  and  slag  were: 
Pig  iron: 


Si 

=0.04    to  3.  7% 

s 

=  0.012    "   0.075% 

p 

=0.017  "  0.029% 

Mo 

=  0.20      "   0.27% 

Gr.  C 

=  3-53     "  3-7«% 

Total  C 

=  3.92     "  5-18% 

Slag: 

SiO2 

=  39-30% 

PA 

=  traces 

MgO 

=  27.06% 

FeO 

=     1.21% 

A1203 

=  18.87% 

CaO 

=  15-55% 

MnO 

=  0.35% 

S 

=  0.32% 

In  regard  to  the  charcoal  used  the  theoretical  amount  neces- 
sary was  determined  as  follows: 
In  i  metric  ton  of  ore  there  are: 

Fe  as  Fe2O3 =     387-94  kgs. 

Fe  "  FeO   =     *79  21  " 

Slag-forming  constituents =     176.00 

From  this  we  may  calculate  the  theoretical  carbon  required: 

387.94  kgs.  Fe  reduced  from  Fe2Os  by  C  forming 

CO  uses =  1 24 . 52  kg.  C 

1 79. 2 1  kgs.  FeO  reduced  by  C  forming  CO  use..  =     38. 35  kg.  C 

162. 87  kg.  C 
567. 12  kgs.  Fe  as  pig  iron  with  47%  require 26.66  kg.  C 

189. 53  kg.  C 
This  equals  ^~^=  334'2  kg>  per  ™^  ^ 


358  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  actual  amount  of  charcoal  used  was  462.67  kg.  con- 
taining 462.67  X  0.559  =  258.64  kg.  carbon.  It  follows  from 
this  that  334.2  —  258.6  =  75.6  kg.  of  the  carbon  necessary  were 
either  replaced  by  the  volatile  constituents  of  the  charcoal,  or 
else  the  CO  produced  reduced  some  of  the  ore  in  the  shaft  of 
the  furnace.  It  is  therefore  clear  that  the  thermal  and  chemical 
processes  taking  place  in  the  shaft  are  of  the  same  nature  as 
those  in  the  ordinary  blast  furnace,  whereby  the  electric  furnace 
is  helped. 

The  small  power  consumption  is  very  remarkable  for  it  only 
slightly  exceeds  the  theoretical,  when  the  melting  of  the  slag  is 
taken  into  consideration.  From  this  it  is  certain  that  the  heat 
is  mostly  used  in  the  interior  of  the  furnace  and  that  because 
of  the  heat  stagnation  near  the  arc  the  brickwork  will  be  strongly 
attacked.  The  test  unfortunately  had  to  be  discontinued  be- 
cause of  the  electrode  not  working  properly. 

Test  No.  14. — (Time  of  test:  64  hrs.,  30  mins.) 

The  results  were: 

4943 . 2  kg.  Blairton  ore  smelted 
2936.95  kg.  charcoal 

338.23  kg.  limestone 

88.71  kg.  sand 

5386.71  kg.  pig  iron  produced 
1968        kw.  hrs.  used  per  metric  ton 

545        kg.  charcoal 

Analyses. 

(a)  The  ore: 
Si02  =6.60% 

Fe2O,  =60.74  \  rv_,c  oco/ 

FeO  =i7.i8[Fe-55'85% 

A1203  =   1.48% 

CaO  =  2.84% 

MgO  =  5-50% 

Mn  =  0.13% 

P2O6  =  0.037%  P=o.oi6% 

S  =  0.57% 

C02  =  4-923% 

and  loss  on  ignition. 


THE  ELECTRO-METALLURGY   OF   IRON  AND   STEEL  359 

(b)  Limestone: 


SiO2 

=   i-7i% 

Fe208  A1203 

=  0.81% 

CaCOs 

=92.  85%  CO  =  51.  96% 

MgCO3 

=  4.40%  MgO="2.og% 

P 

=  0.004% 

S 

=  0.052% 

(c)  Pig  iron  produced: 


Si 

=  3-05    to  5.  15% 

S 

=  0.027  "  0.332 

P 

=  0.024  "  0.037 

Mn 

=  0.07    "  o.i  i 

Graph,  car. 

=  2.72   "  3.46 

Total  car. 

=  3.54   "  4.16 

(<0  Slag: 

Si02 

=  33         to  37% 

A1208 

=  9 

18% 

CaO 

=  18           ' 

30% 

MgO 

=  21               ' 

30% 

MnO 

=    O.OI      ' 

0.05% 

FeO 

=  0.4     ' 

0.9% 

S 

=  2          '3% 

Test  No.  16.— (Time  of  test:  38  hrs.,  20  min.) 
The  results  were: 

2175.6  kgs.  Calabogie  ore  smelted 

1611.7  "    charcoal 
587.9     "    limestone 

34.1     "    quartz 
3246.0     "    pig  iron  produced 
497.0    "    charcoal  used  per  metric  ton 
1970      kw.  hrs.  per  metric  ton 

Analyses. 


(a)  Ore: 

Si02 

=  6.06% 

FezO, 

=58.00  | 

FeO 

=24.78  f 

A120, 

=  1.00% 

CaO 

=  0.40% 

MgO 

=  6.00% 

PA 

=  0.046%  P 

S 

=  0.17% 

CO, 

=  3-544% 

and  loss  on 

ignition. 

=  0.02% 


360   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

(b)  Charcoal: 

Moisture  =   2 . 20% 

Volatile  matter  =20.60% 
Fixed  carbon  =  74 . 40% 
Ash  =  2.80% 

(c)  Lime.— The  same  limestone  was  used  as  in  Test  No.  14. 
No  analysis  was  made  of  the  quartz. 

(d)  Pig  iron  produced: 


Si 

=    1.22     to  2.03% 

s 

=    O.OO6' 

0.008% 

p 

=    0.047 

0.093% 

Mn 

=    0.07 

0.12% 

Graphitic  C 

=    3-87 

4-55% 

Total  C 

=    4.40 

5-o6% 

(e)  Slag  produced: 

Si02  =30-88% 

A1203  =  9-67% 

PA  =  0.014% 

CaO  =36.14% 

MgO  =20.82% 

MnO  =  0.14% 

FeO    '  =  0.73% 

S  =   1.23% 

CRITICISM    OF  IRON   ORE   SMELTING  IN   THE   HE'ROULT 
ELECTRIC  SHAFT   FURNACE 

The  three  tests  given  above  show  the  following  consumption 
of  power  for  the  production  of  one  metric  ton  of  pig  iron: 

Kw.  Hrs.  Charcoal  kg. 
1,726  463 

1,968  545 

1,970  497 

Average  1,888  501 

This  power  consumption  is  good,  exactly  as  in  all  the  former 
tests,  because  the  charge  forms  a  good  heat-insulator.  Still, 
this  concentration  of  heat  has  proved  a  disadvantage,  for  with 
the  great  drop  in  temperature  between  the  arc  and  the  walls  of  the 
furnace  the  limited  amount  of  charge  surrounding  the  arc  is  not 
enough  to  absorb  it,  and  the  result  is  a  rapid  destruction  of  the 
lining  and  uneconomical  operation.  The  ascending  reduction  gases 


THE  ELECTRO-METALLURGY   OF  IRON  AND   STEEL  301 

cannot  lead  away  the  excess  heat  near  the  arc  through  the  charge 
to  the  throat,  so  that  the  lower  part  of  the  furnace  is  necessarily 
quickly  destroyed  by  the  "stagnant  heat." 

The  intended  prereduction  of  the  ore  is  brought  about, 
although  only  to  a  moderate  degree,  so  that  the  carbon  con- 
sumption is  still  high.  The  long  electrode  hanging  in  the  furnace 
is  shown  to  be  a  mistake  because  it  is  continuously  exposed  to 
mechanical  wear,  and  is  also  chemically  attacked  by  the  sur- 
rounding ore  mixture.  Because  of  this  delays  in  operation  may 
be  caused. 

From  all  this  it  follows  that  the  problem  of  electric  ore 
smelting  is  not  to  be  solved  by  this  Heroult  type  of  furnace, 
because  electrode  consumption,  delays  in  operation,  and  the 
lining  costs  exclude  economy.  The  quality  of  the  metal  pro- 
duced, on  the  other  hand,  is  good.  Phosphorus  and  manganese 
are  completely  reduced,  the  slag  can  be  kept  low  in  iron,  and  the 
production  of  low  sulpkur  pig  iron  of  any  desired  silicon  is 
possible.  As  a  reducing  agent  lump  charcoal  and  also  peat  coke 
can  be  used. 

THE  SMELTING  OF  ORE  IN  THE  GRONWALL,  LINDBLAD  & 
STALHANE  ELECTRIC   SHAFT  FURNACE 

Gronwall,  Lindblad  &  Stalhane  knew  that  the  amount  of 
reducing  gases  developed  was  not  sufficient  to  carry  the  excess 
of  heat  present  near  the  arcs  from  the  lower  part  of  the  furnace 
to  the  shaft  where  it  could  be  used  economically  for  preheating 
the  charge.  They  therefore  increase  the  amount  of  gas  by 
forcing  into  the  lower  part  of  the  furnace,  by  means  of  a  fan, 
part  of  the  waste  gases  drawn  from  the  throat.  The  amount 
is  regulated  so  that  the  excessive  heat,  which  would  soon  lead  to 
the  destruction  of  the  lower  part  of  the  furnace,  is  driven  into  the 
shaft. 

Because  of  the  continuous  operating  troubles  experienced 
with  the  long  Heroult  electrode,  Gronwall,  Lindblad  &  Stalhane 
used  three  electrodes  introduced  at  the  sides  of  the  lower  furnace 
in  their  early  tests. 

A  general  view  of  the  furnace  is  shown  in  the  accompanying 


362   KLECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

illustration,  Fig.  124.  In  principle  it  is  similar  to  an  ordinary 
small  blast  furnace,  the  electrodes  taking  the  place  of  the 
tuyeres.  The  extensive  smelting  tests  carried  out  with  all  kinds 
of  ores  allow  a  definite  opinion  to  be  formed  as  to  the  practical 
efficiency  of  this  type  of  furnace,  and  show  that  there  is  no 
more  difficulty  in  'making  iron  with  4  per  cent,  carbon  in  the 
electric  furnace  than  in  the  ordinary  blast  furnace.*  Theor- 
etically, the  direct  production  of  the  harder  steels  is  also  pos- 
sible, but  experience  has  shown  that  such  steels  do  not  have  the 
required  temperature,  and  must  be  tapped  while  thickly  fluid, 
which  leads  to  troubles  in  operation. 

In  regard  to  construction  the  furnace  has  shown  that  the 
expected  advantages  are  obtained.  First  with  reference  to 
avoiding  the  stagnant  heat  in  the  lower  part  of  the  furnace  which 
would  lead  to  rapid  wearing  away.  In  the  first  test  furnaces, 
which  were  built  either  with  none  or  a  very  small  shaft,  the 
reducing  gases  escaped  at  70°  C,  but  with  the  new  construction 
the  gases  at  the  throat  have  a  temperature  of  200°  C.  to  250°  C. 
(see  Fig.  129),  and  the  radiation  loss  of  the  shaft  is  also  equalized 
by  these  hot  gases. 

From  this  it  follows  that  the  lower  part  of  the  furnace  will 
stand  up  better  during  operation,  but  the  efficiency  of  the 
furnace  will  not  be  so  great,  that  is  the  power  consumption 
necessary  per  ton  of  pig  iron  will  be  higher. 

Second,  in  regard  to  preheating  and  preliminary  reduction 
of  the  ore,  while  smelting  the  ore  in  the  electric  furnace,  having 
no  shaft,  only  pure  carbon-monoxide  is  produced,  the  waste 
gases  in  the  electric  shaft  furnace  give  the  following  analysis: 

In  1909  In  ign 

a  Charge  of  Red  Hematite  Fe2O3  Charge  of  Hematite 

CO2  =45%  CO2     CO       H       CH4      N         O 

CO   =40  27.2     57.5     14.8     o.o      0.5      o.o 

H2    =15 

b  Charge  of  Magnetite,  Fe3O4      Charge  of  Magnetite,  Mch.  16  &*  jo 
C02  =30%  C02     CO       H       CH4      N 

12.6     71.9  .  13.0      1.7       0.8 
19.2     59.7     17.6      2.5       i.o 

*  See  American  Electro-Chemical  Society,  p.  400,  1911.     Robertson. 


THE   ELECTRO-METALLURGY   OF  IRON  AND   STEEL 


3f>3 


According  to  the  researches  of  Bauer  and  Glaessner,  the 
reduction  of  iron  ore  by  carbon-monoxide  begins  at  about 
650°  C.,  and  is  most  active  at  about  700°  C. 

On  the  other  hand,  according  to  the  tests  made  at  Trolhattan 
in  1911,  and  given  by  Robertson,  the  reduction  of  magnetite 

m 


FIG.  124. 

by  carbon-monoxide  takes  place  at  as  low  a  temperature  as 
300°  C.  As  the  above  table  shows,  this  furnace  gas  contains 
about  72%  of  that  gas,  so  that  reduction  of  the  charge  by  the 
gas  rich  in  CO  probably  takes  place  throughout  the  whole  of 
the  lower  half  of  the  shaft,  since  the  temperatures  from  the 
official  report  of  the  Jernkontoret  on  the  working  of  the  Trol- 
hattan furnace  for  the  month  of  January,  1911,  gives  a  tempera- 


364   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

ture  at  the  foot  of  the  shaft  (Point  No.  i,  in  Fig.  125)  at  534°  C., 
and  at  point  No.  4  at  351°  C.  The  readings  at  point  No.  5  were 
discontinued,  but  from  the  other  figures  given  it  would  appear 
that  the  temperature  at  this  point  is  not  below  300°  C. 

As  the  gases  in  the  electric  shaft  furnace  leave  the  throat  at 
200°  to  250°  C.,  the  chosen  height  of  shaft  of  5  metres  (16'  4.8") 


FIG.  125.     The  Gronwall,  Lindblad  and  Stalhane  furnace,  design  of  1911. 

is  more  than  sufficient.  With  the  use  of  the  Lange  bell  alone 
this  height  can  be  lowered,  and  with  the  use  of  the  Parry  cone  at 
the  same  time,  the  effective  height  can  be  considerably  decreased. 
The  high  hydrogen  content  of  the  gas  comes  partly  from  the 
hydrogen  contained  in  the  reducing  agents,  but  partly  from  the 
moisture  in  the  charge,  which  is  decomposed.  Hydrogen  does 
not  have  a  special  reducing  action  in  the  presence  of  carbon- 
monoxide,  which  explains  the  given  high  hydrogen  content. 


THE   ELECTRO-METALLURGY   OF   IRON  AND    STEEL  365 

This  is  shown  by  recent  experiments  in  the  production  of  pure 
hydrogen  in  large  amounts  which  consist  of  strongly  heating 
iron  ore  in  a  muffle  furnace,  and  treating  it  with  water-gas.  The 
ore  is  reduced,  yet  almost  the  whole  of  the  hydrogen  passes  from 
the  furnace  unoxidized,  and  is  used  for  heating  the  furnace.  The 
reduced  iron  is  then  employed  to  produce  pure  hydrogen,  by 
passing  steam  over  it. 

That  an  active  prereduction  takes  place  in  the  electric 
blast  furnace  is  proved  by  the  gas  analyses,  and  the  saving 
brought  about  in  this  way  should  be  considered  in  calculating 
the  amount  of  the  reducing  agents  to  be  charged.  This  saving 
is  based  on  the  ratio  of  CO2  to  CO  in  the  waste  gases,  which, 
for  example,  in  the  case  of  magnetite  may  be  40  C02  :  60  CO. 
The  gas  contains  100  carbon  to  140  oxygen,  the  latter  coming 

from  the  magnetite  Fe3  O4,  the  amount  being  ^-  =  35.     This 

4 

is  to  say  that  the  reduction  process  is  based  on  the  formula 
35  Fe804  +  TOO  C.  According  to  this  35  X  3  X  56  parts  of 
iron  and  (iooXi2)+3  parts  of  carbon  should  be  charged  for 
the  production  of  a  pig  iron  with  3%  carbon.  If  the  amount 
of  CO2  in  the  gases  falls  below  30%,  then  there  is  an  excess  of 
raw  material  over  the  carbon  present  for  reduction,  because 
more  ore  enters  the  lower  part  of  the  furnace,  and  some  additional 
material  rich  in  carbon  must  be  charged.  On  the  other  hand, 
if  the  charge  contains  too  much  carbon,  then  the  lower  part  of 
the  furnace  becomes  filled  up  with  it,  and  some  additional  lower 
carbon  material  must  be  charged. 

In  regard  to  the  slag,  a  singulo-silicate  is  the  best,  with  the 
formula  SiO2  2  CaO,  and  the  proper  amount  of  lime  to  produce 
this  must  be  added  to  the  charge.  As  with  the  ordinary  blast 
furnace  so  also  here  it  is  not  profitable  to  run  too  basic  a  slag,  as 
the  power  consumption  increases  more  than  it  should.*  In 
this  case  the  slag  also  very  often  contains  calcium  carbide  formed 
by  the  influence  of  the  arc.  The  power  consumption  per  ton 

*  The  analyses  of  slag,  according  to  Leffler,  which  follow  show  that  these 
have  generally  been  kept  more  silicious  than  desirable  for  the  basic  lining 
of  the  hearth.  This,  however,  has  been  done  for  the  purpose  of  obtaining 


366   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


of  pig  iron  naturally  depends  on  the  amount  of  slag  that  has  to 
be  melted,  because  it  must  be  tapped  in  a  fluid  condition. 

Technical  knowledge  in  1909  was  such  that  only  high  per- 
centage ores  with  65  to  68%  iron  could  be  successfully  smelted, 
which  were  as  low  as  possible  in  sulphur,  and  which  in  no  case 
gave  more  than  10%  of  slag. 

Further  progress  was  made  in  the  1910  and  1911  tests  such 
that  ores  running  as  low  as  53.25%  iron  and  containing  .055  sul- 
phur (Nordmarken  coarse  washed  ore)  were  successfully  smelted. 

Ores  with  high  sulphur  should  therefore  be  roasted  before 
smelting  in  order  to  reduce  the  amount  of  lime  necessary  to  be 
added  to  the  charge.  This  roasting  is  comparatively  easy  with 
ores  with  an  acid  gangue,  an  average  result  with  Swedish  magne- 
tite showing: 

Before  roasting  0.7  %  sulphur 
After  24  hours     0.3  % 

'     48     '          o.i  % 

With  a  large  electric  shaft  furnace  plant  the  waste  gases  can 
be  used  for  heating  the  roasting  furnaces.  Certain  magnetites 
swell  during  roasting,  do  not  break  up,  but  change  into  red 
hematite.  This  change  probably  only  makes  somewhat  lighter 
the  consumption  of  reducing  material  and  electric  energy,  for 
in  the  ordinary  blast  furnace  100  parts  of  magnetite  need  100 
parts  of  coke,  while  the  same  amount  of  red  hematite  takes  90 
parts  of  coke.  Fortunately,  definite  figures  on  this  point  have 
been  obtained  for  electric  furnace  work,  and  are  as  follows : 

These  are  taken  from  the  1910  and  1911  Trolhattan  tests. 
In  those  singled  out  for  comparison  ores  of  about  the  same  iron 
content  (65%)  were  chosen.  The  first  test  lasted  2096  con- 
results  as  closely  comparable  as  possible  with  the  treatment  of  the  same  ores 
by  the  ordinary  blast  furnace  process. 

ANALYSES  OF  SLAG 


Si02 

A12O3 

Ti02 

FeO 

MnO 

CaO 

MgO 

CaS 

Pj05 

Total 

41.60 

6.85 

2.72 

1.49 

I.48 

28.91 

16.70 

.063 

.00 

99.813 

46.82 

5.06 

6.89 

0.23 

33-27 

7-97 

.023 

.041 

100.2 

THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  367 

secutive  hours  and  used  1,760,884  kg.  (about  1,760  tons)  of 
natural  magnetite  ore.  The  charcoal  used  per  ton  of  iron  equalled 
415.7  kg.  (914  lb.),  containing  70.5%  C.  The  second  test  lasted 
193  hours  and  used  223,626  kg.  (about  223  tons)  of  magnetite 
ore  of  which  about  87%  was  roasted.  The  charcoal  used  per 
ton  of  iron  here  equalled  376.3  kg.  (829  lb.),  containing  73.5%  C. 
The  slightly  higher  carbon  in  the  charcoal  content  of  the  latter 
case  is  perhaps  offset  by  only  87%  of  the  ore,  in  this  case  having 
been  roasted,  thus  making  the  comparison  with  raw  and  all 
roasted  ore  better,  and  about  as  it  would  be  if  in  the  one  case 
all  the  ore  had  been  roasted  and  the  charcoal  in  each  case  con- 
tained the  same  carbon  content.  The  reduced  amount  of  char- 
coal used  for  the  roasted  ore  is  about  the  same  as  with  ordinary 
blast  furnace  practise,  viz.  10%. 

Ores  with  a  basic  gangue  give  great  trouble  in  roasting,  for 
the  sulphur  forms  gypsum,  and  the  intended  reduction  in  sulphur 
is  prevented,  therefore  such  ores  high  in  sulphur  should  not  be 
used  in  the  electric  shaft  furnace. 

Fairly  rigid  requirements  are  also  necessary  in  the  physical 
properties  of  the  ore  to  be  smelted.  The  most  suitable  size  is 
that  of  a  large  walnut,  and  only  a  little  pure  ore  should  be 
present.  Lump  ores  have,  therefore,  to  be  crushed  and  none 
can  be  used  which  give  a  considerable  percentage  of  fines  on 
crushing.  This  is  sometimes  a  great  disadvantage  because  of 
the  brittle  character  of  many  magnetites,  etc.  The  reducing 
agent  also  ought  to  be  about  the  size  of  one's  fist,  as  much  as 
possible,  and  fine  material  can  only  be  used  with  difficulty  and 
in  small  amount. 

Formerly,  i.e.,  in  the  earlier  tests  only  charcoal  could  be 
used,  or  a  mixture  of  coke  and  charcoal.  Since  then,  however, 
a  3000  to  3500  HP  furnace  of  the  Gronwall,  Lindblad  & 
Stalhane  type  has  been  completed  and  is  in  operation  at  Har- 
danger,  Norway,  where  English  Durham  coke,  carrying  about  .6% 
sulphur,  is  being  used.  This  is  according  to  Richards,  A.E.C., 
Society,  1911,  p.  417,  and  from  private  advices  from  D.  A.  Lyon. 

In  regard  to  the  practical  operation  in  1909,  small  charges 
had  to  be  used  corresponding  to  the  small  size  of  the  furnace, 


368  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

that  is  to  say,  charges  containing  about  100  kg.  (220  Ibs.)  of 
ore.  In  the  larger  furnace  of  1911  the  average  charge  over  a 
6  months'  period  was  425  kg.  of  ore  (937  Ibs).  One-half  of  the 
ore  should  be  thrown  around  the  outside,  and  the  rest  with  the 
reducing  material  and  lime  in  the  centre.  If  the  charge  were 
placed  only  in  the  centre,  the  1909  furnace  would  easily  hang, 
ordinarily  due  to  the  separation  of  carbon.  Eighty  charges 
containing  8  metric  tons  of  ore  were  smelted  in  24  hours,  which 
with  a  65%  ore  gives  a  total  output  of  5.3  to  5.4  metric  tons  of 
metal,  obtained  at  intervals  of  6  hours.  Because  of  the  small 
amount  of  slag,  it  was  allowed  to  remain  in  the  furnace,  and  was 
tapped  together  with  the  metal. 

The  results  confirm  those  already  obtained  with  the  Heroult 
furnace,  namely,  that  the  smelting  process  is  the  same  as  that 
of  the  ordinary  blast  furnace,  so  that  from  a  corresponding  ore 
any  desired  pig  iron  can  be  obtained  by  running  a  suitable  slag, 
and  regulating  the  furnace  temperature.  With  a  high  tem- 
perature the  iron  contains  more  carbon,  and  if  at  the  same  time 
a  basic  slag  is  run  the  manganese  of  the  ore  is  completely  reduced, 
and  a  low  sulphur  iron  is  obtained  because  of  the  complete  re- 
moval of  the  sulphur  in  the  slag.  The  silicon  content  when 
running  a  basic  slag  and  high  temperature  decreases,  and  under 
these  conditions  a  part  of  the  phosphorus  can  remain  unreduced 
in  the  slag.  On  the  other  hand  if  the  slag  is  acid  the  manganese 
is  partly  slagged  off,  and  with  high  temperatures  a  high  silicon 
iron  is  obtained.  Just  the  same  conditions  obtain  here,  there- 
fore, as  in  the  ordinary  blast  furnace.  In  operation  it  is  always 
desirable  to  produce  an  iron  as  low  in  carbon  as  possible,  which 
is  the  most  favorable  for  foundry  purposes,  and  also  for  subse- 
quent-refining into  steel. 

In  regard  to  power  consumption,  in  the  tests  ending  in  1909, 
280,307  kilograms  of  iron  were  produced  in  1903.5  hours,  during 
5.9%  of  which  no  work  was  done  due  to  troubles  with  the  ma- 
chinery. For  each  metric  ton,  3181  kw.  hrs.  were  used  with  an 
electrode  consumption  of  30  kg.  or  66  Ib.  =  (0.015%),  and  an 
electrode  loss  of  8kg.  or  17.6  Ib.  =  (0.004%).  The  production 
from  the  ore  was  63.5%  and  from  the  charge  60.02%. 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  369 

The  reducing  agent  weighed  354.  kg.  (779.  lb.),  and  con- 
sisted of  41-7%  coke  and  58.3%  charcoal,  and  a  total  of  35.41% 
was  necessary,  which  corresponds  to  a  consumption  of  28%  pure 
carbon.  From  this  data  the  efficiency  of  the  electric  shaft 


FlG.  126.— The  Gronwall,  Lindblad  &  Stalhane  furnace. 
Note  lower  position  of  electrode  clamp. 


Latest  design 


furnace  can  be  calculated.  The  pig  iron  may  be  taken  as  con- 
taining i%  silicon  and  3%  carbon,  which  leaves  96%  iron,  the 
ore  as  magnetite,  and  the  waste  gases  as  containing  30%  CO2 
and  70%  CO. 


370  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

ioo  kg.  of  the  waste  gases  contain  30  +  70  =  100  kg.  carbon, 
and  (2  X  30)  +  70  =  130  kg.  oxygen.  In  the  reduction  of 
magnetite  130/4  kg.  Fe304  must  be  present  to  supply  the  oxygen, 


FIG.  127.— The  Gronwall,  Lindblad  &  Stalhane  furnace.     Gas  circulation 
of  1911. 

and  130/2  =  65  parts  of  silica  to  supply  the  silica.     Reduction 
takes  place  according  to  the  following  formulas : 

1.  —  kg.  Fe3O4  -I-  ioo  kg.  C  =  30  CO2  +  70  CO 

4 
or          13  kg.  Fe3O4  +  40  kg.  C    =12  CO2  +  28  CO 

2.  65  kg.  Si02  +  ico  kg.  C    =  30%  CO2  +  70%  C. 

This  gives  (12  X  12)  -(-  (28  X  12)  =  480  kg.  carbon,  which  ac- 
cording to  the  analysis  of  the  gas  gives  (i2X44)  +  (28X28)  = 

1312  X  ioo 
1312  kg.  gas,  that  is  to  say,  i  kg.  carbon  gives  — 

4°° 

—  kg.  gas.     (i  Ib.  carbon  gives  2.73  Ib.  gas.) 


THE  ELECTRO-METALLURGY   OF  IRON  AND   STEEL  371 

13  kg.  of  magnetite  require  40  kg.  carbon  for  reduction,  so 
that  for  the  smelting  of  13  X  3  X  56  =  2184  kg.  iron  40  X  12  = 

480  kg.  carbon  are  necessary,  or  for  960  kg.  iron  9°°  X  4oQ  _ 
210.99  kg.  2l84 

65  X  28  X  364  kg.  silicon  reduced  from  silica  require  100  X 
12  =  240  kg.  carbon  or  10  kg.  silicon  require  6.59  kg.  carbon. 

For  carburizing  the  iron,  30  additional  kg.  of  carbon  are 
necessary,  so  that  the  total  requirement  of  carbon  necessary  for 
the  production  of  i  metric  ton  of  pig  iron  amounts  to  210.99  + 

6-59  +  3°-°°  =  247-58  kg-  (545-8  lb-)- 

From  this  there  is  formed  (210.99  +  6.59)  X  41.15  = 
594.72  kg.  waste  gases  (1311.1  lb.). 

With  an  output  from  the  charge  of  60%,  960  kg.  iron  require 

.  960  X  100  .    960  X  100 

a  charge  of  —  =  1600  kg.,  with  --  —  --  =  1325.71 

DO  72    X  4^ 

kg.   FesO^     This    will    produce   1600  —  1325.71  =  274.29  kg. 


slag  from  which    --  ^--  =  21.43  kg.    silica  are  reduced  and 

enter  the  iron,  leaving  274.29  —  21.43  =  252.86  kg.  (557.4  lb.). 
Heat  requirements.  —  The  combustion  of  i  kg.  carbon  pro- 
ducing the  waste  gas  analysis  given  above  creates  (0.3  X  8080)  4 
(0.7  X  2470)  =  4153  cals. 


Reduction  of  960  kg.  iron  from  Fe3O4  = 

1648  =  ...........................    1,582,080  cals. 

Reduction  of   10  kg.  Si  from  SiOg  10X7829=  78,290 

Smelting  and   overheating  of   1000    kgs.    pig 

iron  =  1000X280=  .....................         280,000 

Smelting  and  overheating  of  252.86  kgs,  slag 

252.86X595=  ........................         150,452     ' 

Heating  of  594.72  kgs.  CO2  and  CO  to  200°  C. 

594.72X200X0.245  =  ..................  29,145 


2,119,967  cals. 

Heat  Supplied: 

Combustion  of  217.53  kgs.  carbon  =  217. 53  X 

4153  = 903,610  cals. 

Leaving  to  be  supplied  by  the  electric  current 1 ,2 1 6,357 

Total 2,119,967  cals. 


372  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


The  theoretical  amount  of  power  necessary  for  1000  kg.  of  pig 

1.216,^7 

iron  is    '  -  =  1408  kw.  hrs. 

864.5 

As  3181  kw.  hrs.  are  required  daily  per  metric  ton,  the 
efficiency  is g =  44%.    This  low  efficiency  obtained 

in  the  1909  tests  is  for  a  small  test  furnace  run  with  constant 
supervision.  The  remaining  56%  is  lost  by  radiation  and  cooling. 
In  this  respect  measurements  have  shown  that  the  water  cooling 
of  the  three  electrodes  carried  away  about  1 20  kw.  hrs.  per  hour. 
This  gives  a  total  loss  of  1903.5  X  120  for  the  entire  smelting 

test,  which  equals  228,420  kw.  hrs.  or  22g'        =  815.7  kw.  hrs. 

per  metric  ton,  which  corresponds  to —^ =  25.6%  of 

the  electric  energy  supplied.  Through  radiation  alone  56  — 
1 25.6  =  30.4%  of  the  energy  is  lost. 

It  should  now  be  considered 
whether  and  by  how  much  the 
efficiency  can  be  increased  with 
a  larger  plant.  Water  cooling 
will  still  have  to  be  used,  and  in 
this  respect  the  efficiency  can 
scarcely  be  increased.  Apart 
from  this  the  high  water  con- 
sumption, amounting  to  about  % 
gallon  per  second  (2  liters)  is  a 
disagreeable  addition.  On  the 
other  hand  the  radiation  loss 
would  be  smaller  because  the 

cubic  contents  increase  faster  than  the  radiating  surface  of  the 
furnace.  Most  important,  however,  is  the  fact  that  the  smelt- 
ing time  per  ton  of  iron  will  be  lowered,  and  therefore  the  radia- 
tion per  ton  of  metal  will  be  considerably  smaller  with  the 
increase  in  smelting  efficiency. 

Graphite  electrodes  will  increase  the  smelting  efficiency  for 
they  are  better  conductors  than  those  of  carbon,  and  although 


FIG.  128.  —  Modified  gas  circu- 
lation of  1912.  Gronwall,  Lind- 
blad  &  Stalhane  furnace. 


THE  ELECTRO-METALLURCA'  OF  IRON  AND   STEEL 


373 


X 


they  have  a  higher  thermal  loss  (Chapter  VI,  Part  I),  yet  this  is 
more  than  equalized  by  the  increased  efficiency.  At  the  furnace  at 
Falun  carbon  electrodes  were  used,  for  there  is  no  plant  in  Sweden 
making  graphite  electrodes.  This 
dependence  on  electrode  plants  is 
necessarily  very  disadvantageous  for 
all  countries  not  having  them.  Ex- 
periments should  be  made  to  in- 
crease the  life  of  the  electrodes  by 
mechanical  means  as  much  as  pos- 
sible, or  the  electrode  consumption 
is  proportionally  high.  It  will  not 
be  much  lower  with  a  large  furnace, 
as  the  electrodes  are  attacked  be- 
cause of  their  contact  with  the 
ore.  Finally  the  consumption  of 
reducing  material  is  very  much 
higher  than  it  should  be  theoreti- 
cally, which  of  course  is  also  not 
desirable. 

Below  are  given  some  details  of 
recent  test  runs  in  larger  furnaces, 
and  it  may  be  seen  how  these  theo- 
retical considerations  have  worked 
out  in  practise. 

With  regard  to  the  run  from 
Nov.  15,  1910,  to  April  9,  1911,  in 
the  newer  Gronwall,  Lindblad  & 
Stalhane  or  Swedish  Ludvika  Elek- 
trometal  type  furnace,  1882.496  kg. 
(about  1882  tons)  of  iron  were 
produced  in  3501.9  hours,  during 
about  4.4%  or  153.7  hours  of  which 
no  work  was  done  due  to  troubles 
with  the  apparatus.  For  each  metric 
ton,  2391  kw.  hrs.  were  used  with 
an  electrode  consumption  of  10.28 


FIG.  129. —Temperatures  in 
the  Gronwall,  Lindblad  & 
Stalhane  electric  pig-iron  fur- 
nace. 


374  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

kg.  (22.6  Ibs.)  gross,  and  5.27  kg.  (n.6  Ibs.)  net,  per  ton  of 
iron  produced.  The  per  cent,  of  iron  in  the  ore  was  61.54% 
and  the  per  cent,  iron  in  the  charge  57.00%.  The  reducing 
agent  weighed  418  kg.  (920  Ibs.)  per  ton  of  iron  produced  and 
consisted  of  charcoal  only,  having  a  carbon  content  of  80.14%. 
The  pig  iron  may  again  be  taken  as  containing  i%  silicon  and 
3%  carbon,  which  leaves  96%  iron.  The  average  of  the  gases 
produced  consisted  of  23%  CO2,  60%  CO,  10%  H,  2%  CH4,  and 
5%  N.  From  this  data  the  efficiency  of  the  electric  pig-iron 
furnace  may  again  be  calculated  as  before,  and  in  this  case  the 
efficiency  is  considerably  higher,  being  about  59%. 

After  the  furnace  at  Trollhattan  was  shut  down  from  June  to 
September,  1911,  in  order  to  make  such  changes  as  the  operation 
of  the  furnace  had  demonstrated  would  be  beneficial  and  such 
repairs  as  were  necessary,  the  furnace  was  again  put  into  com- 
mission. During  the  run  from  Sept.  3  to  Sept.  30,  537.9  tons 
of  pig  iron  were  produced.  For  each  metric  ton  of  pig  iron  1 749 
kw.  hrs.  were  used  with  an  electrode  consumption  of  less  than 
10  kg.  (22  Ibs.)  gross  and  5  kg.  (n  Ibs.)  net.  The  iron  in  the 
ore  was  67.65%  and  the  iron  in  the  ore  and  lime  was  65.02.  The 
reducing  agent  weighed  only  339.9  kg.  now  (748  Ibs.),  consisting 
of  charcoal.  With  the  same  carbon  content  as  before,  72%,  this 
equals  245  kg.  or  24.5%  pure  carbon.  From  this  data  the 
efficiency  of  the  furnace  can  again  be  calculated  and  figured  out 
to  80.5%.  This  corresponds  to  an  output  of  over  5  tons  of  pig 
iron  per  kilowatt  a  year.  The  above  efficiency  corresponds 
favorably  with  the  Swedish  charcoal  blast  furnace  of  82%  and 
with  70%  the  usual  coke  blast  furnace. 

As  a  conclusion  it  may  be  said  that  the  Gronwall,  Lindblad 
&  Stalhane  electric  shaft  furnace  is  probably  the  first  electric 
furnace  in  which  ore  has  been  smelted  in  some  degree  commer- 
cially. The  weak  point  has  been  the  furnace  roof,  which,  in  the 
1909  furnace,  either  showed  such  small  durability  and  therefore 
made  continuous  operation  impossible,  or  else  had  to  be  cooled 
so  strongly  that  the  efficiency  of  the  furnace  suffered  consider- 
ably. Further  the  close  limits  allowable  in  the  chemical  and 
physical  composition  of  the  charge,  and  the  large  electrode 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  375 

consumption  show  that  the  furnace  can  be  employed  only  under 
especially  favorable  operating  conditions.  The  principle  is  first- 
rate,  especially  with  regard  to  making  the  roof  of  the  lower  part 
of  the  furnace  more  durable,  as  far  as  possible  without  the  use  of 
water  cooling,  and  so  increasing  the  furnace  efficiency.  In  this 
place  the  Lyon  experiments  conducted  at  Heroult,  California, 
with  the  Noble  furnace,  should  be  mentioned.  The  following 
details  are  taken  from  a  paper  by  Otto  Frick,  in  Metallurgical 
and  Chemical  Engineering,  December,  1911,  on  "The  Electric 
Reduction  of  Iron  Ores." 

The  Noble  furnace  is  of  the  same  type  as  that  at  Trollhattan, 
and  like  it  in  all  essential  points.  This,  however,  is  not  the 
result  of  mutual  understanding  or  communication.  An  illustra- 
tion is  given  of  the  furnace  at  Heroult  by  Fig.  130.  This 
furnace  has  now  (191 2)1  been  rebuilt  seven  times.  It  has  three 
single-phase  transformers,  each  of  750  kilo  volt  amperes,  con- 
nected to  a  three-phase  system  of  2200  volts  and  60  cycles. 

The  low  tension  current  is  supplied  to  six  graphite  electrodes. 

These  electrodes  enter  into  the  charge  as  far  as  possible,  and 
in  this  respect  the  practise  differs  from  that  at  Trollhattan,  where 
a  space  is  left  between  the  electrodes  and  the  charge.  The 
pressure  of  the  charge  on  the  electrodes  is  very  nearly  equal  to 
their  breaking  strength,  so  that  the  additional  force  arising  from 
a  sudden  descent  of  the  charge  easily  causes  their  breaking  at 
the  conical  screw  joint.  This  strain  can  be  reduced  approxi- 
mately 30%  by  lowering  the  inclination  from  35°  to  20°,  and 
much  improvement  can  be  made  in  the  joint. 

No  accurate  figures  are  at  hand  as  to  the  power  consumption, 
but  it  has  been  stated  by  the  manager  of  the  plant  that  it  has 
averaged  1940  kw.  hrs.  per  ton. 

With  regard  to  gas  circulation  it  has  been  found  unnecessary 
to  use  any  in  the  Noble  furnace,  where  the  electrodes  penetrate 
the  charge  far  enough  to  prevent  arcing,  so  long  as  they  remain 
unbroken.  The  question  of  the  smelting  of  ore  in  the  electric 
shaft  furnace  can  only  be  considered  solved  when  the  following 
requirements  are  met: 

1  By  1917  the  furnace  had  been  again  entirely  rebuilt. 


376  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

1.  Water  cooling  lowered  as  much  as  possible. 

2.  The  electrode  consumption  lowered,  and  the  electrodes 
done  away  with  as  much  as  possible. 

3.  The  radiation  loss  lowered  by  the  smelting  efficiency  being 
raised  as  much  as  possible. 

4.  The  waste  gases  composed  of  only  pure  carbon-dioxide, 


FlG.  130.— The  Lyon  furnace  in  California. 

of  suitable  temperature,  in  order  to  lower  the  amounts  of  electri- 
city and  reducing  material  necessary. 

Requirements  i  and  2  are  very  closely  connected.     So  long 
as  electrodes  are  used,  cooling  of  the  electrode  heads  cannot  be 


THE  ELECTRO-METALLURGY   OF  IRON  AND   STEEL  377 

avoided,  which  brings  about  great  heat  loss,  and  necessitates  a 
complicated  furnace  construction.  Further  great  durability  of 
the  furnace  lining  is  only  possible  if  the  high  initial  temperature 
of  the  arc  is  avoided,  and  the  most  suitable  moderate  tempera- 
ture used.  This  requirement  is  only  met  by  the  induction  furnace, 
for  on  the  one  hand  electrodes  are  not  used  at  all;  and,  on  the 
other  hand,  as  the  experiments  with  the  hearth  induction  furnace 
have  shown  the  furnace  lining  is  hardly  attacked  at  all  when 
smelting  ore.  An  induction  furnace  with  a  wide  hearth  and  a 
shaft  built  above  is  the  one  to  claim  the  greatest  interest  for 
smelting  ore,  and  so  much  the  more  that  it  can  be  operated  at 
the  highest  temperatures  if  required.  Any  height  of  shaft  can 
be  chosen,  so  that  the  waste  gases  can  be  efficiently  used  for 
prereduction  and  preheating  of  the  charge. 

The  radiation  loss  decreases  with  a  larger  furnace  for  the 
induction  as  for  other  furnaces. 

In  regard  to  the  requirement  that  only  pure  carbon-dioxide, 
at  a  suitable  temperature,  should  be  given  off,  as  waste  gas,  it 
is  well  known  that  carbon-monoxide  loses  the  ability  to  reduce 
ore  when  a  certain  percentage  of  carbon-dioxide  has  been  formed. 
It  is  therefore  theoretically  impossible  to  have  a  product  of  pure 
carbon-dioxide  when  charging  ore  and  fuel. 

The  complete  utilization  of  the  waste  gases  is  therefore  only 
possible  if  they  are  burned  afterwards,  and  used  as  much  as 
possible  for  preheating  the  ore. 

This  preheating  favors  smelting  only  in  that  reduction  is 
made  more  easy  by  an  increase  in  the  degree  of  oxidation,  and 
also  because  the  sulphur  contents  are  lowered  so  that  a  low  sul- 
phur iron  can  be  obtained  without  the  addition  of  more  flux  to  the 
charge.  With  finely  divided  ores  the  roasting  also  brings  about 
a  certain  amount  of  agglomeration  so  that  under  these  con- 
ditions fine  ores,  concentrates,  etc.,  can  be  smelted  in  the  electric 
shaft  furnace.  The  heating  and  agglomeration  of  fine  ores,  if 
sufficient  fluxing  material  is  present,  can  be  carried  out  in  a 
revolving  cylindrical  furnace,  the  ore  being  charged  wet  just  as  it 
comes  from  magnetic  separation  for  instance.  Such  agglomerat- 
ing plants  are  already  in  satisfactory  operation. 


378    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

The  use  of  coal  dust  firing  which  is  recommended  for  the 
heating  of  these  furnaces  is  unsuitable,  as  it  gives  rise  to  high 
fuel  costs,  and  the  ash  of  the  coal  makes  the  ore  higher  in  slag- 
producing  material  so  that  it  is  more  unsuitable  for  electric  fur- 
nace work.  It  is,  therefore,  necessary  to  operate  with  waste 
gases,  and  an  addition  of  producer  gas  should  only  be  made  when 
the  difference  in  price  between  fine  and  lump  ore  is  sufficiently 
great  to  bear  the  increased  cost  in  fuel  needed  for  the  production 
of  the  producer  gas. 

Such  an  ore,  however,  greatly  preheated,  cannot  be  charged 
directly  with  the  reducing  material,  as  it  is  immediately  reduced, 
forming  carbon-monoxide,  and  so  reduces  the  furnace  efficiency. 

The  greatly  heated  ore  must  be  charged  alone,  and  the 
reducing  material  introduced  in  the  hearth  of  the  furnace  at  the 
deepest  zone  of  the  shaft.  The  physical  condition  of  this  re- 
ducing material  is  not  important,  if  solid,  the  most  suitable  size 
is  fine  grained.  Very  small  fuels  and  even  valueless  waste  can 
be  used  with  complete  success. 

Also  fluid- reducing  materials  such  as  tar,  petroleum,  and 
oil  residues  of  all  kinds  can  be  used.  This  is  of  special  interest 
to  those  countries  which  at  present  must  import  coke  or  charcoal, 
because  these  liquid  fuels  due  to  their  high  heating  value  and 
low  ash  contents  are  brought  in  at  much  more  favorable  freight 
rates.  Finally  gaseous  reducing  agents  of  all  kinds  can  be  used, 
such  as  producer  gas.  The  carbon-dioxide  should  be  as  low  as 
possible,  and  if  fuels  with  much  moisture  are  used,  such  as  turf, 
brown  coal,  etc., the  gas  should  be  cooled  as  thoroughly  as  possible 
to  remove  the  moisture  The  troublesome  precipitation  of  tar 
experienced  in  the  cooling  of  producer  gas  is  no  disadvantage  to 
the  electric  furnace,  as  opposed  to  other  furnaces,  for  the  tar  can 
be  collected,  dried  in  centrifugal  machines  and  used  in  the  furnace 
as  a  reducing  agent. 

The  carbon-monoxide  or  the  solid  liquid  or  gaseous  materials 
used  easily  reduce  the  highly  heated  charge,  and  give  warm  waste 
gases  rich  in  carbon-monoxide,  which  can  serve  to  preheat  more 
ore  charges  if  air  is  added  to  combine  with  the  combustible 
constituents. 


THE   ELECTRO-METALLURGY   OF  IRON  AND   STEEL  379 

In  this  way  it  is  possible  to  considerably  reduce  the  consump- 
tion of  reducing  material,  and  to  come  very  near  the  theoretical 
minimum;  which,  in  the  case  of  magnetite  and  the  production 
of  a  pig  iron  with  3%  carbon,  is  143  +  30  =  173  kg.  of  carbon 
(381.4  Ibs.)  per  metric  ton.  The  best  figures  reached  so  far  as 
already  mentioned  are  245  kg.  of  pure  carbon  when  making  a 
pig  iron  with  3.64%  C. 

After  nearly  a  year  of  further  experience  (215  days)  in  operat- 
ing the  furnace  at  Trollhattan,  Leffler  and  Nystrom  contributed  a 
supplementary  report  of  98  pages,  to  the  meeting  of  the  Jern- 
kontoret  at  Stockholm,  on  May  31,  1912.  It  is  not  possible  to 
do  this  report  justice  here  by  any  abstract  of  it,  still  it  may  be 
instructive  to  mention  some  of  the  improvements  recently  made. 
The  new  gas  circulation  system  was  altered  to  better  dry  the 
gas  returned  to  the  furnace.  Fig.  128  shows  the  latest  design 
and  is  but  little  different  from  its  predecessor  shown  by  Fig. 
127.  The  cooler  acts  on  the  condenser  system  and  requires  100 
liters  of  water  per  minute  to  reduce  the  temperature  of  the  gas 
so  that  its  moisture  content  is  reduced  from  4  grams  per  cubic 
meter  to  .5  gram. 

Both  high  and  low  grade  ores  were  used  in  this  run,  so  that 
the  furnace  output  dropped  to  about  15  tons  daily  from  its 
normal  capacity  of  20  tons.  This  run  again  demonstrated  that 
economical  operations  need  a  rich  ore. 

Fig.  129,  which  is  reproduced  from  the  July,  1912,  Metallurgi- 
cal and  Chemical  Engineering,  shows  the  temperature  and 
reaction  in  the  furnace  shaft.  This  abstract  goes  on  to  say: 

The  temperatures  of  iron  and  slag  issuing  from  the  furnace 
varied  as  follows: 

Iron 1230°  to  1420°  C. 

Slag 1290°  to  1460°  C. 

A  large  table  gives  the  temperatures  taken  at  8  points  in  the 
shaft,  just  inside  the  wall  and  in  the  middle;  also  the  percent- 
ages of  CO2  in  the  gases  at  these  different  points. 

There  are  various  not  very  important  irregularities  in  the 
figures,  but  the  general  average  shows  temperatures  up  to  985° 
n  the  middle  at  the  lower  part  of  the  shaft  and  585°  half  way 


380   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

up;  while  near  the  wall  it  is  420°  to  565°  at  the  lowest  hole  and 
down  to  15°  at  the  highest. 

The  measured  percentage  of  C02  shows  that  reduction  takes 
place  ordinarily  only  one-quarter  way  up  the  shaft  at  the  sides 
and  a  little  over  one-half  way  up  in  the  centre. 

The  extent  of  the  zone  of  reduction  by  CO  is  clearly  shown 
in  Fig.  129,  in  which  also  some  temperatures  are  indicated. 

Cooling  Water. — The  contacts  and  jackets  through  which  the 
electrodes  worked  were  water  cooled.  The  heat  carried  away 
thus  varied  from  172  to  288  kw.,  or  10.47  to  I9-3°  (average 
14.50)  per  cent,  of  the  power  used. 

Thermal  Balance. — The  heat  balance  per  1000  kg.  of  pig  iron 
is  worked  out  for  the  four  weeks,  Sept.  3  to  Oct.  i,  1911,  in  which 
the  average  power  used  (high  tension  side)  was  1407  kw.,  and 
the  power  consumption  1749  kw.  hours  per  ton  of  pig  iron;  the 
ores  worked  were  the  rich  Tuolluvaara  ores.  The  heat  balance 
is,  per  kg.  of  iron: 

Combustion  C  to  CC>2 567  calories 

Combustion  C  to  CO 381 

Electric  energy 1 504 


2452  calories 

Consumed  in  reductions 1620  calories 

Decomposition  of  limestone 35 

Evaporation  of  water 24 

Sensible  heat  in  throat  gases 26 

Sensible  heat  in  slag 75 

Sensible  heat  in  pig  iron 300 

Cooling  water 195 

Lost  in  transformers 43 

Lost  in  conductors 44 

Radiation  and  conduction 90 

2452  calories 

The  authors  then  make  some  interesting  calculations,  the 
results  of  which  are,  in  brief,  as  follows:  The  gas  kept  in  cir- 
culation was  2.28  times  the  gas  normally  produced  and  escaping. 
Assuming  this  gas  to  enter  the  furnace  at  22°  and  to  enter  the 
shaft  at  1000°,  it  carried  into  the  shaft  as  sensible  heat  343,118 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL 


381 


calories  per  ton  of  iron,  or  22.9  per  cent,  of  all  the  heat  electrically 
generated  in  the  crucible.  Since  it  carried  with  it  22.5  kg.  of 
water  vapor  and  174  kg.  of  CO2,  both  of  which  are  decomposed 
by  the  glowing  carbon,  the  net  heat  absorbed  in  these  decom- 
positions is  160,283  calories,  or  10.7  per  cent,  of  the  electric 
energy  used.  The  gas  circulation  therefore  transferred  physically 
and  chemically  33.6  per  cent.  =  1/3  of  the  electrical  energy 
used  from  the  crucible  into  the  shaft  of  the  furnace. 

Some  later  operating  data  are  published  by  Orten-Boving,  in 
the  Canadian  Engineer,  of  May,  1914,  of  these  furnaces  when 
making  electric  pig  iron  of  three  qualities  as  follows : 


Si—  % 

Mn—  % 

P-% 

S-% 

For  open  hearth  treat- 
ment   
For    Lancashire    treat- 

.40-   .60 
2O—     30 

.30-    .50 
2O—     30 

.oii-.oi8 
01  i—  018 

.015 
.015—  .020 

For  Bessemer  treatment 

I  .  OO-I  .  40 

2.50-3.00 

.015-.  019 

.005 

Experience  has  shown  that  a  much  more  constant  product 
is  obtained  from  the  electric  than  from  the  old  blast  furnaces, 
one  of  the  reasons  for  this  being  the  large  receiver  in  the  lower 
part  of  the  furnace  which  acts  as  a  regulator  of  the  quality. 
The  reason  for  the  high  Si  and  Mn  in  the  Bessemer  pig  is  that 
the  temperature  of  the  electro-Bessemer  pig  is  lower  than  the 
ordinary  Bessemer  pig  from  blast  furnaces.  The  experience 
obtained  points  to  the  following  results:  It  is  cheaper  to  make 
spiegel  than  gray  pig  because:  i.  More  current  can  be  put 
through  the  furnace.  2.  The  current  consumption  is  lower. 
3.  Thus  the  production  is  higher.  4.  The  electrode  consump- 
tion is  lower.  5.  The  repair  costs  are  lower.  The  quality  of 
the  pig  is  not  influenced  by  the  percentage  of  iron  contents  of 
the  ore. 

The  electrode  consumption  has  been  comparatively  high, 
being  influenced  by  the  following: 

i.  High  power  consumption.  2.  Too  lively  gas  circulation 
and  too  large  percentage  of  CO2  in  the  gas.  (The  carbon  con- 


382   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

sumption  is  correspondingly  lower.)  3.  Too  large  carbon 
electrodes  for  the  load.  Recently  the  gas  from  the  furnaces  has 
been  used  as  fuel  under  the  open  hearths,  and  this  is  valued  at 
50  to  75  cents  per  ton  of  electric  pig  produced.  The  influence 
of  electric  pig  in  finished  steel  shows  that  the  change  tends  to 
make  better  steel.  Some  of  the  larger  furnaces  are  designed  for 
8,000  h.p. 

It  was  found  that  when  using  coke  instead  of  charcoal  it  is 
better  to  operate  on  burnt  lime,  to  keep  the  power  consumption 
down,  the  latter  rising  when  too  much  CO2  is  produced. 

Eighteen  of  these  furnaces  are  now  in  operation  or  building, 
all  in  Scandinavia.  It  has  been  found  that  the  operation  of  the 
electric  reduction  furnace  is  much  simpler  than  that  of  a  blast 
furnace.  Less  labor  is  required  and  no'  more  skill  is  necessary 
than  with  a  blast  furnace.  The  total  initial  cost  per  ton  of 
output  is  also  lower. 

For  a  plant  of  three  furnaces  of  3,000  h.p.  capacity  each,  the 
following  staff  and  labor  would  be  required :  One  chief  engineer, 
one  assistant,  two  chemists,  three  foremen,  two  electricians,  ten 
men  in  each  of  three  shifts.  Below  is  given  the  results  of  a  fur- 
ther continuous  run  of  one  furnace  belonging  to  Stromsnas  Jern- 
werks  A.  B.  from  October  i,  1912,  to  September  i,  1913,  3,000  h.p. 

Number  of  charges 26,549 

Weight  of  ore  used,  tons  .  (metric) 1 1,338 

Weight  of  limestone,  tons 907 

Weight  of  charcoal,  tons 2,700 

Produced  pig  iron,  tons 7,258.3 

Weight  of  charcoal  used  per  ton  of  pig  iron,  Ib 830 

Total  number  of  hours  when  running  normal,  hr. .  .  .  7,957 

Total  power  consumed,  kw.-hr 1 5,291 

Total  power  consumed  per  ton  iron,  kw.-hr 2,107 

Weight  of  pig  iron  produced  per  I  h.p.  yr.  tons 3 .05 

Weight  of  pig  iron  produced  per  I  kw.-yr.,  tons 4 .14 

Total  consumption  of  electrodes,  tons 28.42 

Consumption  of  electrodes  per  ton  of  pig  iron  pro- 
duced, Ib ...  8.7 

Details  of  part  of  this  run  are  as  follows: 
Continuous  Run  of  the  Trolhattan  Furnace  for  Three-Month 
Periods  from  October  i,  1912,  to  June  30,  1913. — (This  furnace 


THE   ELECTRO-METALLURGY  OF  IRON  AND   STEEL 


383 


was  run  by  the  Swedish  Association  of  Iron  Masters  with  a  view 
to  establishing  the  practical  success  of  the  system  as  well  as 
to  give  the  various  members  an  opportunity  of  trying  their 
various  kinds  of  ore. .  Thus,  in  the  table  below  different  kinds 
of  ore  were  used  during  the  period  indicated.) 

The  ore  from  Kiruna  and  Tuollavara  is  of  the  highest  quality 
obtainable  in  Sweden.  It  will  be  seen  that  the  output  of  the 
furnace  as  well  as  the  consumption  of  electrodes  depends  largely 
on  the  quality  of  the  ore  used. 


Period 

Oct.  i,  1912 
to 
Dec.  31,  1912 

Jan.  i,  1913 
to 
March  31,  1913 

April  I,  1913 
to 
June  30,  1913 

Number  of  charges 

6,193 

7,107 

7,28l 

Kiruna  A  ore    '  .tons 

1,047 

223.3 

799.8 

Tuollavara  ore  tons 

973-4 

123-3 

762.6 

Klacka-Lerberg  ore  tons 

885.6 

1,453 

1,426.5 

Persberg  ore  tons 

8.82 

47-97 

148.4 

Total  ore  tons 

2,914.8 

3,047-6 

3,137-4 

Limestone                                  tons 

169.94 

252.8 

273-5 

Charcoal                               .  .tons 

699 

719 

738 

Pig  iron  produced  tons 

1,905.86 

1,933-32 

2,000.14 

Charcoal  per  ton  pig  iron  .  .  .  .  Ib. 

825 

835 

830 

Actual  working  time  hr 

2,158-5 

2,113-7 

2,147 

Consumed  power,  kw.-hr.  ..  units 

3,957,565 

4,095,588 

4,216,544 

Consumed  power  per  ton  .  .  units 

2,076 

2,118 

2,108 

Produced  pig  iron  per  kw.- 

year                                 •  •  •  tons 

4.22 

4.14 

4-15 

Produced  pig  iron  per  h.p.- 

year  tons 

3.10 

3-04 

3.05 

Consumption  of  electrodes, 

total  tons 

5-307 

8.670 

7.896 

Consumption    of    electrodes 
per  ton  Ib 

(2.78kg.)6.2 

(4.5kg.)  10.  o 

(4  kg.)     8.8 

Each  of  the  above  furnaces  now  has  six  round  electrodes. 

The  Noble  Electric  Steel  Company  at  Heroult,  California, 
through  their  manager,  Crawford,1  publish  results  of  their  tests 
and  operation,  while  still  making  foundry  pig  iron.  During 
1916-17  they  changed  to  making  80%  ferro-manganese  which 

i  Metallurgical  and  Chemical  Engineering,  page  383,  July  I9I3- 


384      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

they  are  doing  with  4,700  kw.-hr.  to  the  net  ton  of  2,000  lb.,  or 
5,170  kw.-hr .  per  metric  ton.  The  plant  consists  of  one  2,ooo-kw. 
and  one  3,ooo-kw.  iron  furnace,  substantially  as  per  Fig.  131, 
and  the  usual  auxiliary  apparatus.  To  make  this  installation 
an  economic  success  caused  many  misgivings. 

"With  approximately  the  same  costs  for  power,  charcoal,  and 
stock,  local  conditions  caused  them  to  abandon  the  type  of 
furnace  operating  commercially  in  Sweden. 

"If  a  certain  type  of  furnace  is  found  to  be  best  suited  to 
make  a  grade  of  iron  for  which  the  demand  is  limited,  either  a 
market  must  be  found  for  this  product,  and  that  market  edu- 
cated to  accept  it,  or  else  the  design  of  the  furnace,  or  method 
of  operation  must  be  altered  so  as  to  make  a  grade  of 'iron  for 
which  there  is  a  market  already  established.  In  Sweden,  con- 
ditions permitted  them  to  adopt  the  former  and  simpler  course, 
while  at  Heroult  they  had  to  resort  to  the  latter. 

"The  principal  users  of  pig  iron  on  the  Pacific  slope  and  far 
Western  States  are  custom  foundries.  Specialty  foundries,  such 
as  those  making  stoves,  bath  tubs,  pipe,  etc.,  are  still  relatively 
few,  as  are  also  open~hearth  steel  furnaces,  so  that  to  operate 
electric  furnaces  successfully  on  the  Pacific  Coast,  grades  of 
iron  must  be  produced  which  meet  the  demands  of  general 
foundry  purposes. 

"There  is  on  the  coast  an  abundance  of  scrap  cast-iron,  and 
foundries  making  what  are  spoken  of  in  the  East  as  heavy 
castings  are  few  in  number;  hence  the  popular  demand  is  for  a 
soft  high-silicon  iron  which  is  a  good  scrap  carrier  and  can  be 
easily  machined  when  in  light  castings. 

"Thus  it  is  apparent  their  problem  became  one  not  merely  of 
making  pig  iron  successfully  but  of  making  iron  with  a  silicon 
content  of  from  2  to  3  per  cent,  economically.  When  a  blast 
furnace  works  "off "  it  ordinarily  means  only  a  slight  concession 
in  price  to  get  rid  of  the  low-grade  iron,  while  with  them  if 
iron  runs  under  i  per  cent,  silicon  it  means  a  large  concession 
in  price  to  dispose  of  it.  As  electric  furnaces  like  blast  furnaces 
have  the  faculty  of  misbehaving  at  times,  conditions  imposed  on 
them  the  necessity  of  having  a  furnace  which  would  respond 


THE   ELECTRO-METALLURGY   OF   IRON  AND    STEEL  385 

readily  to  alterations  in  the  furnace  burden  and  still  be  of  large 
enough  capacity  to  be  efficient. 

"The  following  analysis  represents  the  magnetite  ore  used: 

Si02 3.43% 

A12O3 0.81% 

CaO 0.70% 

Mg° 0.32%        Fe 67.86% 

Mn° 0.28%        P 0116% 

CuO Trace          S 021% 

Fe304 79.63% 

FeA. 14-56% 


99-73% 

"This  magnetite   lies   between  quartz  and  limestone,  the 
analysis  of  the  latter  is  as  follows: 


A12O3  ............................................     0.61% 

MgO  ............................................     1.12% 

CaO  ............................................  53.80% 

FeO  .............................................  20% 

C02  (by  diff.)  ....................................  43-25% 


100.00% 

"The  first  furnace  closely  resembled  the  Swedish,  although 
independently  designed,  and  was  operated  intermittently. 

"But  from  the  style  of  its  construction,  it  is  apparent  that  it 
could  not  be  made  to  respond  readily  to  changes  in  the  burden, 
and  in  order  to  make  consistently  high-grade  foundry  iron  this 
is  an  essential.  In  a  blast  furnace,  too  great  an  excess  of  coke 
in  the  burden  can  be  taken  care  of  by  increasing  the  quantity 
of  air  blown  in,  but  in  an  electric  furnace  this  is,  of  course,  not 
feasible,  as  the  oxygen  would  attack  the  electrodes.  The  excess 
of  carbon  must  be  taken  care  of  by  an  excess  of  oxygen  put 
into  the  furnace  through  increasing  the  ore  in  the  burden. 

"The  necessary  excess  one  might  think  could  be  calculated  to 
a  nicety,  but  because  of  unknown  factors  practically  the  excess 
must  be  added  gradually  until  the  controls  on  the  slag  from 
the  iron  and  the  general  working  of  the  furnace  show  the  desired 


38G       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

result  to  have  been  accomplished.     This  sometimes  takes  several 
days. 

"If  the  excess  of  carbon  has  been  allowed  to  proceed  too  long, 
the  furnace  will,  of  course,  'freeze  up.'  The  slag  will  give 
up  part  of  its  lime  content  to  form  calcium  carbide,  part  of  its 
alumina  to  form  aluminium  carbide,  part  of  its  silica  to  form 
silicon  carbides,  and  part  to  form  ferro- silicon,  and  part  of  the 
carbon  remaining  turns  to  beautiful  sparkling  flakes  of  graphite. 
Remarkable  examples  of  molecular  replacement  of  the  carbon 
in  the  charcoal  by  silicon  carbide  has  also  been  noted,  making 
beautiful  specimens  of  petrified  charcoal.  Once  a  furnace 
presented  these  phenomena,  though  there  is  no  excuse  for  it, 
as  the  decrease  in  the  amount  of  stock  going  into  the  furnace 
and  the  daily  controls  on  the  slag  and  metal  should  give  ample 
warning.  The  matter  of  too  little  carbon  gives  less  trouble, 
and,  if  the  furnace  is  producing  low  silicon  and  carbon,  iron 
should  give  none  at  all. 

"The  question  may  be  fairly  put:  Why  cannot  the  necessary 
carbon  in  the  burden  be  calculated  within  sufficiently  close 
limits  to  prohibit  any  possibility  of  trouble?  Theoretically,  of 
course,  it  can  be.  By  daily  analyses  of  the  furnace  gases  taken 
at  regular  distances  as  they  ascend  from  the  crucible  up  the 
stack  the  ratio  in  which  the  carbon  is  actually  being  oxidized 
to  CO  and  CO2  can  be  approximately  determined,  and  this, 
together  with  the  controls  on  the  slag  and  metal,  will  keep  the 
carbon  within  safe  limits  if  the  furnace  is  running  with  a  low 
carbon  burden;  that  is,  making  low-silicon  iron 

"When,  however,  the  furnace  is  running  on  a  high  carbon 
burden,  calculated  to  make  a  3  per  cent,  silicon  iron,  it  is  ap- 
parent that  the  carbon  must  be  carefully  regulated.  Insuffi- 
cient carbon  not  only  lowers  the  grade  of  the  iron,  but  intro- 
duces difficulty  by  throwing  an  excess  of  SiO2  into  the  slag. 
Too  much  carbon  lowers  the  efficiency  of  the  furnace  besides 
leading  to  the  difficulties  mentioned  above. 

Practically,  it  is  always  necessary  to  carry  an  excess  of 
carbon  over  theoretical  calculations  to  take  care  of  the  atmos- 
pheric oxygen  and  moisture  which  is  occluded  in  the  charcoal 


THE  ELECTRO-METALLURGY  OF   IRON  AND   STEEL  387 

and  the  atmospheric  air  which  is  inevitably  drawn  into  the 
furnace  after  it  has  been  in  use  in  spite  of  every  practical  pre- 
caution to  prevent  it.  It  is  evident,  of  course,  that  these  are 
to  a  considerable  extent  unknown  factors;  hence  the  charcoal 
must  be  continually  varied,  as-  the  control  analysis  indicates 
that  it  is  too  high  or  too  low. 

"So,  while  the  shaft  type  of  furnace  gave  promise  of  economic 
success,  it  operated  on  the  low-silicon,  low-carbon,  white  iron 
(which  our  Swedish  friends  have  dignified  by  the  name  of  pig 
steel), -it  was  shut  down  for  making  foundry  iron." 

The  present  long  and  narrow  type  furnace  was  designed 
by  Frickey  and  others.  It  is  5.04  meters  (16'  6")  long,  2.36 


i 

FIG.  131. — Sections  of  No.  7  Furnace. 


meters  (7'  9")  wide,  and  3.10  meters  (10'  2")  high.  It  has  four 
electrodes  delta  connected  and  five  charging  shafts  5.5  meters 
(18')  high,  as  shown  by  Fig.  132.  This  type  of  furnace  seems 
best  adapted  to  this  class  of  service.  The  3,ooo-kw.  furnace 
is  8.54  meters  (28')  long  and  3.05  meters  (10')  wide.  The  stacks 
are  widened  toward  the  bottom,  as  in  Fig.  131,  to  prevent  the 
burden  from  hanging.  Between  the  stacks  the  top  of  the 
furnace  is  arched,  and  through  the  center  of  these  arches  the 
electrodes  penetrate  vertically  into  the  charge.  Acheson  graph- 
ite electrodes,  305  millimeters  (12")  diameter,  are  used,  using 
the  tapered  M.  &  F.  joint. 


388   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

So  far,  no  arrangements  have  been  made  here  to  utilize  gases, 
for  the  best  way  to  utilize  these  had  to  be  studied,  rather  as 
an  economic  than  a  metallurgical  problem;  i.e.,  whether  the 
saving  in  charcoal  effected  by  circulating  the  gases  back  through 
the  furnace  and  taking  advantage  of  the  reducing  action  of 
the  CO  is  greater  than  the  saving  in  fuel  by  burning  them 
under  lime  kilns,  charcoal  retorts,  or  elsewhere.  Observations 
led  to  the  adoption  of  the  latter  course. 

Considering  the  claims  made  for  the  cooling  effect  of  the 


FIG.  132. 

circulated  gases  on  the  furnace  roof,  this  is  hardly  deemed  worthy 
of  practical  consideration  on  this  resistance  type  furnace.  If 
the  charge  is  descending  regularly  it  will  protect  the  roof  and 
if  it  is  not,  the  slight  lowering  of  temperature,  caused  by  the 
cool  gases,  will  not  prevent  the  heat  radiated  from  the  electrode 
from  melting  the  roof. 

Three  750  KVA.  transformers  furnish  three  phase  delta 
current  between  40  and  80  volts,  using  15  steps. 

The  electrode  holders  are  water-cooled  cylindrical  stuffing 
boxes  made  of  98%  copper.  The  electrodes  are  suspended  in 
these  from  above  and  the  annular  space  between  the  electrode 
and  the  holder  is  packed  with  a  specially  prepared  graphite 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  389 

capable  of  being  compressed  to  a  density  equal  to  that  of  the 
electrode  itself.  This  packing  material  offers  no  more  resistance 
to  the  passage  of  the  current  than  the  electrode,  and  because  of 
its  unctuous  nature  permits  the  electrode  to  be  raised  and  lowered 
without  breaking  electrical  contact. 

From  an  electrical  standpoint  this  type  of  furnace  has 
worked  very  smoothly.  The  instruments  show  but  little  varia- 
tion, when  things  are  normal,  except  that  the  power  factors 
(which  average  respectively  90,  85  and  70  per  cent.)  improve 
after  the  furnace  is  tapped  and  gradually  fall  off  again  as  the 
molten  iron  accumulates  at  the  bottom. 

METALLURGY 

"The  stock  is  charged  into  the  five  charging  stacks  previously 
mentioned  on  the  basis  of  5oo-lb.  units  of  iron  ore.  This  small 
charging  unit,  while  it  entails  extra  labor  on  the  feed  floor,  has 
the  advantage  of  mixing  the  ore,  charcoal,  and  flux  as  inti- 
mately as  if  the  charge  were  bedded,  and  homogeneity  of  charge 
is  very  essential. 

"With  this  type  of  electric  furnace  at  least  the  ore  is  reduced 
to  a  very  much  greater  extent  by  actual  contact  with  the  carbon 
than  by  the  action  of  the  CO  in  the  stack  gases.  Some  examples 
of  gas  analyses  will  bear  this  out." 

Gas  Analyses 

CO2  O                     CO                   CH4                   H 

8.6  0.2  57.2                  16.0                  0.8 

9.2  1.4  56.2                   12.2                   1.2 

7-8  0.15  57.1 

6.0  0.20  67.9 

8.1  o.io  64.8 

4.2  0.25  60.7 
5.0  o .  40  66 . 6 

From  these  analyses  it  will  be  noted  that  the  ratio  of  CO  to 
CO2  is  very  high,  but  by  utilizing  the  calorific  value  of  the  gas, 
the  high  charcoal  consumption  will  be  balanced  to  a  very  ap- 
preciable extent. 


390      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Experiments  have  been  made  to  some  extent  with  the  pos- 
sibility of  utilizing  coke  or  gas  carbon  instead  of  charcoal. 

However,  the  72-hour  metallurgical  coke,  as  tried,  offers  two 
objections: 

First,  its  electrical  conductivity  is  so  good  that  much  of 
the  current  passes  between  the  electrodes  in  the  upper  part  of  the 
furnace.  The  smelting  zone  is  thereby  raised  and  the  furnace 
runs  hot  on  top  with  attendant  melting  of  the  arches  and  cold 
at  the  bottom. 

Second,  this  coke,  because  of  its  density  and  high  crush- 
ing strain  does  not  break  down  like  charcoal  as  the  burden 
descends;  hence,  less  surfaces  of  carbon  are  exposed  to  be 
oxidized  by  the  ore  and  there  is  a  less  intimate  mixture  of 
the  two.  Reduction  of  the  ore  takes  place  more  slowly,  the 
silicon  in  the  iron  is  lowered,  the  power  consumption  per 
ton  increases,  and  thus  the  efficiency  of  the  furnace  is  re- 
duced. However,  by  adopting  certain  precautions  in  crushing 
the  stock  and  feeding  same  into  the  furnace  operated  on  a 
mixture  of  60%  coke  and  40%  charcoal  with  a  very  fair  degree 
of  furnace  efficiency  and  the  grade  of  the  iron  was  kept  up  to 
No.  2  foundry. 

The  possibilities  of  operating  electric  iron  furnaces  with 
coke  instead  of  charcoal  seem  to  offer  a  very  interesting  and 
necessary  field  for  investigation.  At  present  successful  opera- 
tion of  electric  iron  furnaces  depends  among  other  things  on 
an  abundant  and  fairly  cheap  supply  of  charcoal.  This  gen- 
erally limits  their  field  of  activity  to  well-timbered  regions 
which  are  usually  isolated  and  where  freight  rates  are  high. 
Many  of  our  coals  which  make  a  very  poor  metallurgical 
coke  for  blast  furnace  use  on  account  of  their  low  crushing 
strain  might  be  found  to  make  a  satisfactory  fuel  for  electric 
furnace  use. 

The  fact  that  the  ore  is  of  so  high  a  grade  renders  the  metal- 
lurgical problem  somewhat  different  from  that  usually  en- 
countered. The  ore  as  it  comes  from  the  quarry  will  often  run 
for  weeks  at  a  time  as  low  as  2^2%  SiO2,  and  from  67  to  68% 
Fe;  so  that  to  make  pig  iron  which  will  run  from  2  to  3%  Si, 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  391 

it  is  necessary  to  augment  the  silica  in  the  ore  by  the  addition 
of  barren  quartz.  The  requisite  amount  of  lime  or  limestone 
is  added  so  as  to  give  theoretically  a  slag  running  about  47% 
SiO2.  The  following  slag  analysis  will  indicate  the  extent  of 
the  silica  variation: 

SiO2  A12O3  FeO  CaO  MgO 

54.00  29.70  1.30  12.98  1.17 

50.20  28.60  2.40  16.03  2.36 

46.13  27.20  0.65  23.10  3.31 

Ordinarily  slags  containing  more  than  50%  Si02  are  too 
viscous  to  run  well,  but  the  slags  are  fluid  up  to  54%  SiO2. 
This  may  be  due  to  the  high  alumina  ratio.  As  only  from  125 
to  140  Ibs.  of  slag  per  ton  of  pig  is  made  it  is  found  more  eco- 
nomical to  permit  a  small  percentage  of  the  iron  to  escape  in  the 
slag  than  to  attempt  to  reduce  it.  The  depth  of  the  green  color 
in  the  slag  also  serves  as  a  rough  indication  for  the  furnace-men 
as  to  whether  the  carbon  ratio  of  the  burden  is  becoming  too 
high  or  too  low. 

In  calculating  the  charcoal  for  the  burden  it  is  assumed  that 
all  the  carbon  burns  to  CO,  as  it  is  necessary  anyway  (for 
reasons  previously  given)  to  carry  an  excess  of  charcoal  in 
order  to  make  high  silicon  iron.  Thus,  to  make  2.75  silicon  iron 
the  theoretical  quantity  of  charcoal  (containing  85%  fixed 
carbon)  necessary  is  35%  of  the  pig,  whereas  there  is  actually 
used  about  40%.  Inasmuch  as  any  necessary  change  in  the 
burden  is  distributed  over  five  stacks  the  furnace  responds  very 
rapidly  and  practically  permits  of  the  silicon  in  the  iron  to  be 
controlled  within  a  limit  of  0.5%. 

The  iron  is  tapped  three  times  a  day  into  sand  pig-beds.  A 
sample  is  taken  from  each  bed  from  a  pig  250  millimeters  (10 
inches)  long  cast  for  the  purpose.  The  system  of  grading  is 
somewhat  like  that  used  in  grading  the  Southern  iron,  ex- 
cept that  it  is  graded  entirely  by  silicon  content  as  the 
sulphur  and  phosphorus  run  uniformly  under  0.04%  when 
operating  on  charcoal  alone.  The  pig  is  sold  on  a  guar- 
anteed silicon  content  with  0.25%  limits.  The  grade  card  is 
as  follows: 


392      ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Silicon  Per  Cent. 

No.  I  Silvery 4.5  5.0 

No.  2  4.0  4.5 

No.  i  Soft 3.5  4.00 

No.  2   "  3.0  3.5 

No.  I  Foundry  High 2 . 75  3 .  oo 

No.  I         "         Low 2.50  2.75 

No.  2         "         High 2.25  2.50 

No.  2         "         Low 2.00  2.25 

No.  3         "         High 1.75  2.00 

No.  3         "         Low 1.50  1.75 

No.  4  High 1 . 25  i .  50 

No.  4   •     "        Low i. oo  1.25 

Some  tests  were  made  to  determine  the  relative  variation  of 
the  silicon  and  carbon  as  the  burden  carbon  content  increases  or 


§5.5 

3t      ^  5.0 

33      a4.5 

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32      ItO 

31      "  3.6 



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26      »  1.0 

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108       110 


GRAPHIC  ILLUSTRATION 


JttetalTap  98         98        100        102      104       106 

Percentage  of  Carbon  in  Iron. 

Percentage  of  Silicon  in  Iron. 

_._  Percentage  of  Carbon  to  Ore. 

:  Showing  the  reeponie  of  the  Carbon  and  Silicon  in  the 
Iron  to  variations  of  the  Charcoal  ratio  in  the  burden.. 
Starting  with  a  cold  furnace. 


118       120      122       121     126 


FlG.  133. — Variation  of  Silicon  and  Carbon. 


decreases.  Some  of  these  results  are  shown  by  Fig.  133.  Each 
number  represents  a  metal  tap  made  at  regular  8-hour  intervals. 

While  the  silicon  responds  readily  to  the  carbon  ratio,  the  latter 
shows  but  little  variation.  The  slag  analyses  were  not  noted  at 
this  time.  The  fracture  of  this  iron  is  much  finer  and  more  uni- 
form than  that  of  charcoal  blast  furnace  iron  of  the  same  grade. 

A  very  noticeable  characteristic  is  the  homogeneity  of  the 
fracture  and  the  almost  entire  absence  of  segregations  and 
"hard  spots."  It  is  also  distinguished  by  its  toughness,  so 
that  it  has  to  be  cast  with  very  deep  notches. 


THE    ELECTRO-METALLURGY   OF   IRON  AND    STEEL  393 

The  softer  irons  have  already  won  a  reputation  for  themselves 
as  softeners  and  scrap  carriers.  Some  analyses  taken  at  random 
of  car-load  lots  of  high,  medium,  and  low-grade  iron  will  illustrate 
how  constant  all  the  other  metalloids  are  except  the  silicon. 

Analysis  on  a  2oo-ton  lot  shipped  to  a  foundry  for  making 
steel  castings  and  sold  on  a  guarantee  of  from  2.75  to  3%  silicon 
and  a  maximum  of  0.04  %  of  sulphur  and  0.04%  of  phosphorus. 

Silicon 2  88% 

Combined  carbon 0.09% 

Graphite  carbon 3  38% 

Sulphur 0.028% 

Phosphorus 0.031% 

Analysis  on  a  ico-ton  lot  shipped  for  general  foundry  pur- 
poses— silicon  guaranteed  from  2.25  to  2.50%: 

Silicon 2.42% 

Combined  carbon 0.27% 

Graphite  carbon 2 . 94% 

Sulphur 0.036% 

Phosphorus 0.023% 

Analysis  on  a  ico-ton  lot  shipped  to  stove  works  to  be 
mixed  with  high  phosphorus  iron  for  stove  castings  and  sold  on 
guarantee  of  from  1.75  to  2.00%  silicon  and  0.04%  phosphorus. 

CONCLUSION 

The  efficiency  of  this  type  of  furnace  increases  slightly  more 
than  the  direct  ratio  to  the  increase  in  load  and  it  is  of  interest 
to  note  that  as  in  the  case  of  the  electric  steel  furnaces,  the 
faster  the  furnace  is  operated,  the  cooler  the  walls  and  roof  are, 
and  the  smoother  it  operates.  Crawford  offers  the  explanation 
that  the  faster  smelting  takes  place  the  faster  the  cool  charge 
can  descend  to  protect  the  arches  and  walls.  The  long  and 
n'arrow  type  furnace  is  not  equal  technically  in  its  efficiency  to 
the  shaft  type  carrying  the  same  load,  though  the  power  con- 
sumption has  been  as  low  as  2,200  kw.-hr.  per  ton  when  carrying 
3,oookw.,  but  this  type  offers  the  possibility  of  building  several 
furnace  units  on  to  each  other,  like  copper  blast  furnaces.  This 
decreases  the  radiation  and  electrical  losses.  A  bank  of  three 
or  four  units  arranged  in  this  way  will  admit  of  as  simple 


394  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

metallurgical  control  as  a  single  unit  and  will  have  an  efficiency 
equal  to  a  shaft  type  of  furnace  carrying  the  same  load. 

Further,  it  can  be  arranged  so  that  part  of  the  furnace  can  be 
frozen  up  and  repaired  while  the  remainder  is  operating,  and 
for  this  reason  its  yearly  output  should  exceed  the  shaft  type. 

From  the  nature  of  its  construction  it  is  capable  of  being 
made  more  nearly  fool-proof  metallurgically,  mechanically,  and 
electrically  than  the  shaft  type,  and,  further,  the  electrode  con- 
sumption is  lower,  due  to  the  fact  that  the  electrodes  penetrate 
vertically  into  the  charge. 

While  it  is  hardly  agreed  with  the  prophecies  made  by  some 
that  electric  furnaces  for  producing  pig  iron  will  eventually  be  com- 
petitors of  blast  furnaces  even  in  the  regions  where  economic  con- 
ditions make  the  latter  possible,  Crawford  feels  that  where  electric 
power  can  be  obtained  cheaply  and  where  coke  and  freight  rates 
are  high  and  for  making  superior  grades  of  iron,  electric  reduction 
furnaces  will  enable  many  large  bodies  of  iron  ore  to  be  worked 
which  would  otherwise  remain  idle  and  that  the  electric  iron  fur- 
nace, both  of  the  shaft  type  and  of  the  long  and  narrow  type, 
each  in  the  field  best  adapted  for  it,  will  make  steady  progress. 

The  work  of  Turnbull1  in  making  low  phosphorous  pig  iron 
deserves  considerable  attention,  even  though  its  manufacture 
has  been  curtailed  since  the  close  of  the  Great  War.  This  is 
made  in  a  stationary  three-electrode  three-phase  furnace,  solid 
bottom,  1 200  kw.,  much  resembling  the  Heroult.  Wlien  using 
shell  turnings  for  raw  material,  about  500  kw.  hrs.  were 
needed  per  metric  ton  and  only  9.5  kg.  of  amorphous  carbon 
electrode  (2 1  Ibs.) .  Ferro  silicon  was  replaced  by  another  product, 
which  reduces  the  cost  and  helps  the  carbon  content.  Twenty- 
five  consecutive  heats  had  the  following  average  analysis: 

Carbon  Silicon  Manganese          Sulphur  Phosphorus 

3.19  1.16  .70  .014  .020 

This  grade  of  pig  iron  was  also  made  from  a  mixture  of 
50%  metallic  turnings  and  50%  iron  ore,  necessitating  about 

1  Robert  Turnbull,  A.E.S.,  Oct.,  1917,  and  Oct.,  1918,    "Electric  Pig   Iron 
After  the  War." 


THE   ELECTRO-METALLURGY   OF   IRON   AND   STEEL          395 

1400  kw.  hrs.  per  metric  ton.  This  furnace  was  of  the  batch 
process  and  not  of  the  continuous  type.  With  1200  kw. 
it  could  produce  30  tons  per  day  with  a  batch  process  furnace 
using  all  scrap,  but  20  tons  using  half  scrap  and  half  ore  with 
the  continuous  type  on  account  of  the  higher  load  factor.  With 
the  latter  process  no  ferro  silicon  or  fluorspar  would  be  required, 
and  the  return  in  metallic  contents  charged  would  be  100% 
as  against  90%  with  turnings  alone;  besides  a  saving  in 
furnace  repairs,  this  would  probably  more  than  compensate 
for  the  extra  power,  electrodes,  and  carbon  necessary  for  the 
reduction  of  the  ore.  A  mixture  of  this  kind  permits  the  use 
of  iron  ore  concentrates,  the  charge  being  kept  porous  enough 
by  the  presence  of  the  turnings,  and  as  these  concentrates  can 
be  obtained  very  low  in  phosphorus,  they  could  be  used  to  ad- 
vantage in  the  production  of  low  phosphorous  iron  and  permit 
the  use  of  turnings  with  higher  phosphorous  contents.  As  the 
operation  would  be  conducted  in  a  reducing  atmosphere,  the 
resulting  carbon  in  the  iron  would  be  perfectly  comparable 
to  the  blast  furnace  product. 

THE  FUTURE  OF  ELECTRIC   STEEL 

This  is  well  discussed  by  Matthews,1  and  in  comparing  it  with 
the  crucible  process,  especially  in  reference  to  the  possibility  of 
replacing  crucible  steel,  he  stated,  "The  point  is  that  each  proc- 
ess has  its  peculiar  field,  and  while  some  crucible  tonnage  may 
be  diverted  to  electric  steels;  yet  it  is  more  likely  that  electric 
steel  will  find  its  market  in  the  most  exacting  requirements  of 
steel  for  structural  and  tensile  purposes,  such  as  have  come  about 
almost  simultaneously  with  the  processes  themselves,  namely,  for 
automobile  and  airplane  parts.  Crucible  steels  for  these  pur- 
poses are  scarcely  commercial  because  of  the  difficulties  at- 
tendant upon  making  very  low  or  medium  carbon  alloy  steels  by 
that  method,  and  the  tonnage  demanded  far  beyond  what 
could  be  met  by  crucible  steels.  However,  experience  has 

1Dr.  John  A.  Matthews,  A.E.S.,  Oct.,  1918;  also  A.I.  and  S.I.,  May,  1916, 
"The  Electric  Furnaces  in  Steel  Manufacture." 


.300     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

shown  that  the  electric  furnace  was  apparently  invented  to  meet 
a  new  demand  rather  than  to  replace  an  old  process."  Robin- 
son1 presents  a  paper  on  the  "Triplexing  Process  of  Producing 
Electric  Steel  at  South  Chicago."  This  represents  the  largest 
tonnage  installation  of  electric  steel  in  the  world  (3-25  ton  and 
2-15  ton).  He  said:  "The  luxury  of  to-day  is  the  necessity 
of  to-morrow.  Safety  cannot  be  measured  by  price,  and  public 
opinion  will  more  and  more  insistently  call  for  the  highest  ex- 
cellence in  the  automobile  and  airplane  and  other  forms  of 
fabricated  material."  During  the  years  that  the  Halcomb  Steel 
Co.  was  alone  in  the  electric  furnace  business  in  the  United 
States,  it  was  very  hard  to  convince  users  of  its  superior 
quality,  and  still  harder  to  get  makers  of  open-hearth  steels  to 
admit  it.  Robinson's  experience  confirms  what  others  have  been 
contending  for  many  years. 

MAKING  PIG   STEEL  IN  THE  ELECTRIC   FURNACE 

Some  experiments  have  been  made  on  a  very  small  scale  by 
Keeney.1  Whether  pig  steel  (carbon  less  than  2.2%)  ever  becomes 
a  product  on  a  large  scale  depends  almost  entirely  on  whether 
or  not  it  can  compete  with  the  other  processes.  At  Degerfors, 
Sweden,  it  was  found  that  pig  steel  was  more  suitable  for  mak- 
ing steel  in  the  open  hearth  than  ordinary  pig  iron,  requiring  less 
time  for  refining.  Normal  pig  iron  made  in  the  electric  furnace 
was  found  to  be  less  suited  to  the  production  of  open  hearth  steel 
than  normal  blast  furnace  pig  iron.  This  shows  the  advantage  of 
producing  pig  steel  rather  than  pig  iron  in  the  electric  furnace, 
when  steel  is  to  be  the  final  product.  His  summary  is  as  follows : 

i.  In  the  electric-furnace  production  of  pig  steel  from  ore, 
carbon  in  the  product  can  be  kept  below  2.2%,  and  regulated  to 
an  extent  by  the  amount  of  carbon  charged,  without  result- 
ing in  excessive  loss  of  iron  in  the  slag  or  in  the  produc- 
tion of  a  pig  steel  very  high  in  impurities,  if  a  fair  grade 
of  ore  is  used. 


*T.  W.  Robinson,  May,  1918,  A.I.  and  S.I. 
2  A.  I.  M.  E.,  Feb.,  1014. 


THE    ELECTRO-METALLURGY    OF    IRON    AND    STEEL  397 

2.  It  is  not  difficult  to  slag  the  greater  part  of  the  silicon, 
phosphorus,  and  sulphur  of  the  charge,  if  the  furnace  is  hot 
and  the  slag  fluid,  but  conditions  are  less  favorable  to  the  slagging 
of  sulphur  than  of  other  impurities  in  the  operation  of  an  electric 
furnace  for  pig-steel  production,  which  is,  of  course,  contrary 
to  experience  in  the  manufacture  of  pig  iron. 

3.  The  loss  of  iron  in  the  slag  should  not  be  excessive  unless 
the  pig  steel  produced  is  of  very  low  carbon  content. 

4.  From  the  results  with  the  Domnarfvet,  Trollhattan,  and 
Heroult  furnaces,  there  does  not  appear  to  be  great  difficulty  at- 
tending the  production  of  pig  steel  in  an  electric  shaft  furnace, 
and,  in  fact,  experience  has  shown  that  there  is  less  diffi- 
culty in  the  operation  of    the  electric  furnace  on  pig  steel 
than  on  pig  iron. 

5.  At  any  place  where  there  is  a  market  demand  for  steel 
and  pig  iron  can  be  made  in  the  electric  furnace  at  a  profit,  the 
steel   ultimately  produced  would  be  cheaper,  if  made  by  the 
electric  reduction  of  iron  ore  to  pig  steel,  followed  by  refining 
in  another  furnace  if  necessary,  than  if  the  product  of  the  electric- 
reduction  furnace  was  pig  iron  to  be  subsequently  converted 
to  steel  in  another  furnace. 

Among  other  tests  made  are  those  by  Humbert  and  Hethey.1 
These  tests  were  made  in  a  6-ton  Heroult  steel  furnace.  The 
results  of  their  tests  are  given  in  the  table  on  page  374. 

The  electrode  consumption  was  between  32  and  36.3  kg.  per 
ton  of  steel  made.  The  wear  of  the  furnace  lining  was  about 
the  same  as  when  melting  scrap.  When  all  the  ore  is  reduced 
the  slag  should  be  taken  off  and  the  charge  treated  as  with  an 
ordinary  pig  and  scrap  charge. 

Their  conclusions  and  economic  advantages  are  as  follows: 

The  authors  have  come  to  the  conclusion  that  with  the  aid 
of  the  modern  electric  furnace,  and  given  satisfactory  conditions, 
the  economic  manufacture  of  steel  direct  from  ore  is  a  practical 
possibility.  The  material  produced  will  be  superior  to  that 
manufactured  by  present  methods,  and  will  have  properties 

^r.  Iron  &  Steel  Ins.,  May,  1914- 


ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


SERIES  A 

B 

c 

Hard 
Steel 
Kg.,  etc. 

Rail 
Steel 
Kg.,  etc. 

Soft 
Steel 
Kg. 

Tool 
Steel 
Kg.,  etc. 

Soft 
Steel 
Kg. 

•6^OO 

S8SO 

s6so 

43OO 

CGOO 

Scrap  used 

2OO 

2OO 

I2OO 

200 

Coke 

I2OO 

IOOO 

93° 

75O 

1050 

Lime 

95° 

IOIO 

1035 

95O 

250 

Steel  made  .  

3600 

3630 

358o 

2970 

3269 

Scrap  made  

120 

85 

10 

215 

90 

Loss  in  per  cent  

6-5 

4.16 

4.66 

18.0 

2-54 

Electricity 

consumed  per 

ton  in  kw.-hr  

•2459 

2862 

2843 

2604 

2709 

Time,  hours  

16 

18.35 

18.45 

H-iS 

14.40 

Carbon  

1-39 

.56 

.23 

.89 

.27 

Phos 

OSS 

O2  T. 

OIS 

OI4. 

031 

Analysis  • 

s 

0^8 

027 

O7O 

O^7 

os8 

Si  

•13 

.15 

.11 

.10 

•05 

Mn  

.26 

.28 

•47 

.27 

•3i 

80%  FeMn  used  

12 

25 

7-5 

17-5 

40%  FeSi 

used  

20 

ii 

10%  FeSi 

used  

5° 

20 

Fluorspar. 

20 

of  the  greatest  importance  and  value  to  the  steel  user.  A  special 
type  of  furnace  will  probably  be  developed,  although  the  standard 
Heroult  furnace  is  satisfactory  for  occasional  charges.  The 
charge  should  lie  deep  in  the  furnace,  to  permit  violent  ebullition 
of  the  bath  without  overflowing.  Anthracite  electrodes  will 
probably  be  found  most  satisfactory  owing  to  their  freedom  from 
breakages.  The  best  use  for  this  process  will  be  found  in  coun- 
tries that  possess  readily  available  sources  of  water  power  together 
with  deposits  of  pure  rich  ores.  Charcoal,  coke  or  anthracite 
coal  can  be  used  as  fuel.  In  countries  where  cheap  power,  pro- 
duced from  waste  heat  such  as  blast-furnace  gases,  coke-oven 
gases,  etc.,  can  be  obtained,  its  most  useful  sphere  will  probably 
be  found  in  making  high  grade  steels  for  springs,  drills  and  similar 
tools,  shafts,  and  all  grades  requiring  exceptional  toughness. 

The  econpmic  advantages  of  this  process  are:     i.  One  opera- 
tion instead  of  several.     2.  One  furnace  instead  of  a  large  and 


THE   ELECTRO-METALLURGY   OF  IRON  AND    STEEL  399 

complicated  plant.  3.  Simplicity,  cleanliness  and  ease  of  control 
of  electricity  as  a  source  of  fuel  and  power.  4.  Ability  to  use 
refractory  and  richer  ores,  such  as  titaniferous  magnetites,  etc. 
5.  Freedom  of  the  steel  from  impurities.  6.  Speed  of  manu- 
facture. 7.  General  cost  depends  largely  on  cost  of  electric 
power,  but  will  be  cheaper  than  the  electrical  production  of  steel 
from  pig  iron.  8.  Less  labor  needed.  9.  Metallurgical  sim- 
plicity of  the  process.  10.  Efficient  control  of  quality  of  steel 
to  be  obtained,  both  from  an  analytical  and  physical  point  of 
view.  The  steel  made  in  these  tests  was  of  excellent  quality. 

THE  USE  OF  THE  ELECTRIC  FURNACE  FOR  MELTING,  FOR  RE- 
FINING PIG  IRON,  AND  FOR  THE  PRODUCTION  OF 
ORDINARY  AND  SPECIAL  QUALITY  STEEL 

Pig  iron,  that  is  the  iron  and  carbon  alloy,  produced  in  the  elec- 
tric or  ordinary  blast  furnace  or  in  any  way,  contains  other  con- 
stituents, such  as  silicon,  manganese,  sulphifr,  phosphorus,  copper, 
arsenic,  etc.,  which  come  from  the  charge.  Some  of  these  ele- 
ments, such  as  copper  and  arsenic,  are  easily  reduced  from  the  ore 
and  enter  the  metal,  and  cannot  be  removed  economically  by  any 
metallurgical  operation.  The  other  elements,  such  as  silicon,  man- 
ganese, sulphur,  and  phosphorus,  can  be  partly  eliminated  in  the 
blast  furnace  and  slagged  off,  and  they  can  also  be  separated  more 
or  less  from  the  finished  metal  by  later  metallurgical  operations. 

If  the  amount  of  one  of  these  constituents  is  to  be  lowered 
in  order  to  make  the  metal  more  suitable  for  any  special  purpose 
it  is  spoken  of  as  a  refining  of  the  metal.  Therefore,  a  lowering 
in  the  carbon  percentage  of  the  metal  is  also  to  be  considered 
as  a  refining.  The  refining  process  can  be  of  various  kinds, 
reducing  and  oxidizing,  or  consist  of  simple  reactions  such  as: 

FeS  +  Mn  =  MnS  +  Fe. 

If  an  electric  furnace  is  to  be  suitable  for  refining,  then  all 
processes,  whether  oxidizing  or  reducing,  must  be  practicable; 
above  all,  it  must  allow  the  carrying  out  of  all  metallurgical 
operations,  such  as  are  now  used  in  the  open  hearth,  converter, 
etc.  The  electric  furnace,  and  this  must  be  specially  pointed 


400  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

out,  should  not  be  different  from  an  ordinary  furnace,  except 
that  the  heating  is  electro-thermal.  The  electric  furnace,  as 
such,  except  for  the  lining,  should  have  no  influence  on  the 
chemical  composition  of  the  bath  of  metal.  Arc  furnaces  do 
not  correspond  altogether  to  these  requirements,  for  an  influence 
of  the  electrodes  on  the  bath  cannot  be  avoided  even  with 
careful  operation. 

Electric  heating  of  the  furnace  has  the  great  advantage  that 
the  influence  of  the  hot  gases  on  the  charge,  which  is  present 
in  the  furnaces  used  now,  is  excluded,  so  that  work  can  be 
carried  out  with  an  oxidizing,  neutral,  or  reducing  atmos- 
phere at  will.  Even  the  maintenance  of  a  neutral  or  reduc- 
ing atmosphere  is  not  only  very  difficult  with  the  present 
furnaces  but  really  impossible,  except  with  crucible  and  muffle 
furnaces. 

The  induction  furnace  completely  meets  these  requirements, 
for  in  it  a  reducing  or  oxidizing  atmosphere  can  be  obtained  as 
desired.  With  the  arc  furnace  on  the  other  hand,  reduction 
processes  take  place  very  well,  but  oxidation  processes  only 
slowly,  due  to  the  reducing  action  of  the  electrodes,  and  with 
an  increased  use  of  oxidizing  material  there  is  more  electrode 
consumption.  Otto  Thalner  gives  expression  to  this  in  his 
address  before  the  "  Oberschlesischen  Bergwerksverein  deutscher 
Chemiker,"  1909,  when  he  says:  "The  arc  furnace  is  indeed  a 
good  reduction  furnace,  but  a  bad  refining  furnace."  An  electric 
furnace,  however,  to  answer  all  requirements  should  allow  reduc- 
tion and  oxidation  processes  to  be  carried  out  equally  well,  and 
this  should  be  pointed  out  before  anything  is  said  about  the 
metallurgy  of  iron  and  steel,  the  influence  of  impurities,  or  the 
refining  of  the  metal. 

Phosphorus. — This  exists  in  the  iron  in  the  form  of  phosphide 
of  iron  which  dissolves  in  the  metal  bath  without  difficulty  up 
to  1.7%  Phos.,  forming  mixed  crystals.  Phosphorus  segregates 
in  both  pig  iron  and  steel,  for  the  phosphide  has  the  comparatively 
low  melting  point  of  910°  C.  For  instance,  in  gray  foundry 
iron  the  well  known  separated  bean-shaped  pieces  are  sometimes 
found,  which  give  the  following  analyses: 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  401 


I 

I                                           2 

3 

Bean-shaped  pieces 1.30%  P  1.30%  P  1. 00%  P 

Solid  piece  near  the  beans.  .  I        0.60%  P  0.55%  P  0.50%  P 


Analytical  proof  of  its  segregation  in  steel  is  given  in  the 
next  section  under  Sulphur. 

If  a  section  is  cut  from  a  steel  high  in  phosphorus,  polished 
and  etched  with  a  solution  of  copper-ammonium-chloride,  by 
Professor  Heyn's  method,  the  places  rich  in  phosphorus  will  be 
colored  dark,  and  one  is  in  a  position  to  determine  the  segregation 
in  the  material.  As  segregated  material  has  considerably  lower 
physical  properties  than  normal  material,  a  low  phosphorus 
should  be  specified  if  a  high  quality  is  desired,  so  that  if  ordinary 
high  phosphorus  material  is  to  be  used  for  making  high  quality 
steel,  it  must  be  dephosphorized.  In  order  to  do  this  an  Ameri- 
can has  proposed  to  destroy  the  phosphide  by  the  addition  of 
another  element  according  to  the  equation: 

Iron  phosphide  +  metal  =  iron  +  metal  phosphide. 

Naturally  a  metal  must  be  chosen  that,  in  the  form  of  phos- 
phide, does  not  alloy  with  the  iron  but  goes  into  the  slag.  Such 
reactions  are  theoretically  possible,  and  have  been  carried  out 
practically  to  a  small  extent.  Even  the  silica  holding  desul- 
phurizing slags  of  the  electric  furnace  show  a  certain  content  of 
phosphides,  'which  can  be  easily  recognized  by  the  garlic-like 
smell  when  the  slags  are  moistened  with  water,  but  this  method 
of  dephosphorizing  has  not,  so  far,  become  of  practical  import- 
ance. 

The  removal  of  phosphorus  is  only  possible  with  certainty, 
at  present,  when  the  phosphorus  is  oxidized  to  phosphoric  acid, 
combined  with  lime,  and  removed  as  slag.  The  phosphorus  is 
oxidized  at  low  temperatures  before  the  carbon,  but  at  higher 
temperatures  only  after  the  removal  of  the  carbon  from  the 
bath.  One  can  therefore  dephosphorize  high  carbon  charges 
without  having  to  previously  completely  remove  the  carbon. 
In  this  case  the  temperature  of  the  bath  should  be  kept  low,  an 


402   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

easily  fusible  basic  slag  charged  rich  in  oxide  of  iron,  and  at  the 
end  of  the  dephosphorization  immediately  tapped.  To  a  certain 
degree  this  method  of  dephosphorizing  requires  considerable 
care  and  experience  for  complete  success,  although  the  melting 
of  high  carbon  heats  is  economical. 

Dephosphorization  is  more  certain  with  low  carbon  and  very 
high  temperature,  and  at  the  same  time  strongly  oxidizing  and 
basic  slags.  Further,  the  oxidation  of  the  phosphorus  can  be 
brought  about  as  well  by  the  oxygen  in  the  ores  as  by  that  of 
the  air.  The  maintaining  of  a  basic  slag  naturally  requires 
that  the  work  be  done  on  a  basic  hearth. 

Sulphur. — Sulphur  can  exist  in  steel  as  MnS,  as  well  as  FeS. 
The  latter  can  alloy  with  liquid  iron  while  the  former  does  not 
alloy  with  the  liquid  metal,  and  is  therefore  only  present  in  the 
form  of  included  material.  If  the  bath  of  metal  is  allowed  to 
stand  long  enougty,  then  the  MnS  will  rise  to  the  surface  because 
of  its  lower  specific  gravity,  and  can  be  drawn  off.  This  is  not 
possible  with  the  remaining  FeS  which  remains  alloyed  with  the 
liquid  metal.  For  this  reason  the  slags  which  separate  from 
the  metal,  for  example  from  basic  Bessemer  iron,  in  casting 
ladles,  or  mixers  contain  a  high  percentage  of  sulphur  and  also 
manganese,  present  for  the  most  part  as  MnS,  while  the  amount 
of  iron  is  not  so  great.  This  is  shown  by  the  following  average 
analysis  of  ladle  slag: 

Iron 6% 

Manganese 42% 

Sulphur 10% 

If  these  slags  come  lower  in  sulphur,  then  oxidation  of  the  sulphide 
of  manganese  by  the  air  or  by  included  oxide  has  taken  place.  A 
high  manganese,  however,  is  always  a  characteristic  of  these 
slags  so  that,  after  a  preliminary  roasting,  they  can  be  used  in 
the  blast  furnace  as  an  ore  of  manganese. 

Sulphur  is  harmful  to  pig  iron,  steel,  and  wrought  iron,  the 
reason  probably  being  the  low  freezing  point  of  FeS,  whereby 
during  the  cooling  of  the  bath  of  metal  it  segregates  to  the  centre, 
and  also  brings  about  the  red  short  character  of  high  sulphur 
material. 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  403 

It  is  therefore  necessary  to  desulphurize  the  iron  as  much  as 
possible  before  it  is  made  into  steel,  a  process  that  is  carried  out 
by  the  addition  of  ferro-manganese  to  the  liquid  bath,  if  there 
is  not  enough  manganese  already  present.  The  sulphide  of  iron 
is  then,  decomposed  according  to  the  equation: 

FeS  +  Mn  =  MnS  +  Fe 

and  if  sufficient  time  is  given  the  MnS  rises  to  the  surface  of  the 
bath  into  the  slag  and  can  be  removed.  The  process  only  takes 
place  smoothly  if  a  considerable  excess  of  manganese  is  used. 
Even  in  this  case,  however,  no  total  desulphurization  is  possible. 
The  sulphur  can  only  be  lowered  to  a  certain  degree,  about 
0.05%,  which  is  still  considerably  too  high  for-  special  quality 
steel. 

In  liquid  pig  iron  or  steel,  rich  in  manganese,  that  has  stood 
long  enough  before  pouring,  the  sulphur  is  to  be  thought  of  as 
being  present  exclusively  in  the  form  of  FeS.  If  a  microscopic 
section  is  taken  from  high  sulphur  material,  polished  and  etched 
as  described  under  "phosphorus,"  and  the  dark  segregation 
places  examined,  then  a  considerably  higher  sulphur  content  is 
found  than  in  the  ground  mass,  but  only  the  same  manganese. 
If  the  segregation  were  a  question  of  the  separation  of  MnS 
then,  with  an  increasing  sulphur  content,  there  would  also  be 
noticed  an  increase  in  manganese,  which  is  not  the  case. 

Below  are  given  some  analyses: 

First  material: 

Mn%  S%  P% 

Pure  ground  mass 0.48  0.067  0.050 

Segregate 0.48  O.182  o.ioo 

Second  material: 

1.  Very  black  segregate.  0.30  0.097  0.155 

2.  Gray  segregate 0.30  0.055  °-°79 

3.  Pure  material 0.30  0.040  0.047 

The  elongated  sulphide  inclusions  often  seen  under  the 
microscope  that  are  usually  assumed  to  be  MnS  are  perhaps 
nothing  more  than  inclusions  of  sulphur  holding  slag,  which 
during  the  rolling  of  the  hot  ingot  were  not  yet  solidified  in  its 


404  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

interior  and  therefore  were  rolled  out.  Also  the  general  appear- 
ance of  red  short  material  during  forging  and  rolling  inclines 
one  strongly  to  the  opinion  that  the  Fe  — FeS  alloy  separates 
between  the  crystals  but  not  inside  the  crystals  themselves. 

As  already  mentioned  liquid  steel  produced  in  the  ordinary 
way  and  therefore  fairly  high  in  sulphur  must  be  further  de- 
sulphurized for  the  production  of  good  quality  steel.  For  this 
purpose  the  electric  furnace  is  suitable.  The  following  two 
processes  are  those  mostly  used  for  desulphurizing  in  the  electric 
furnace,  and  both  take  place  most  energetically  at  high  tempera- 
tures. They  also  both  require  the  use  of  a  neutral  or  reducing 
atmosphere  in  the  furnace  and  the  melting  of  a  strongly  basic 
slag. 

In  order  to  make  these  basic  slags  easily  fusible  additions  of 
fluor-spar,  and  quartz  in  the  form  of  sand,  are  made. 

(1)  The  use  of   the   chemical   reaction  FeS  +  CaO  +  C  = 
Fe  +  CaS  +  CO. 

For  carrying  out  this  reaction,  therefore,  the  help  of  carbon 
is  necessary,  and  the  process  can  be  operated  very  satisfactorily 
in  the  arc  furnace,  due  to  the  favorable  influence  of  the  electrodes. 
Carbon  must  be  added  to  the  bath,  and  for  this  reason  the 
process  is  used  only  when  it  is  a  question  of  the  production  of 
high  carbon  steels.  In  melting  very  soft  steels,  one  must  either 
take  into  account  a  certain  carbonization  of  the  bath  and  later 
remove  the  carbon,  or  else  be  satisfied  with  a  less  complete 
desulphurization.  Even  if  the  carbon  is  only  thrown  on  the 
slag  covering  from  time  to  time,  a  certain  absorption  of  carbon 
by  the  bath  cannot  be  avoided. 

(2)  The  use  of  the  chemical  reaction  between  silicon  and 
sulphur  whereby  SiS  is  produced  which  escapes  as  gas. 

FeS  +  Si  =  Fe  +  SiS. 

If  at  the  same  time  a  lime  carrying  slag  is  formed  on  the 
metal  bath  a  further  desulphurization  takes  place  according  to 
the  equation : 

2  FeS  +  2  CaO  +  Si  =  2  Fe  +  2  CaS  +  SiO2. 
The  CaS  is  removed  as  slag.     It  is  interesting  to  know  that 


THE   ELECTRO-METALLURGY  OF  IRON  AND  STEEL  405 

both  reactions  take  place  almost  quantitatively  so  that  scarcely 
more  than  the  theoretical  amount  of  ferro-silicon  must  be  added 
to  the  bath,  and  if  desired  a  low  silicon  steel  can  be  produced. 
The  process  is  often  used  in  the  induction  furnace  and  has  the 
advantage  that  it  can  be  used  equally  well  for  high  and  very  low 
carbon  heats.  The  reaction  gives  a  very  fluid  slag  because  of 
the  increase  in  the  amount  of  silica. 

Moreover,  fluor-spar  is  also  an  equally  good  desulphurizing 
agent  when  ferro-silicon  is  used,  according  to  the  equation : 
2  FeS  +  2  CaF2  +  Si  =  Fe  +  2  CaS  +  SiF4. 

Further,  in  regard  to  desulphurization  by  means  of  silicon 
in  the  electric  furnace  a  great  many  theoretical  reactions  have 
been  suggested,  a  small  selection  from  which  is  given  below. 

(a)  With  the  use  of  burned  lime. 

1.  2  CaO  +  SiS  =  CaS  +  SiO2  +  Ca  -,   but   there    would 
result 

Ca  +  Fe  S  =  CaS  +  Fe. 

2.  2  CaO  +  2  SiS  =  2  CaS  +  Si02  +  Si  -,  but  there  would 
result 

Si  +  FeS  =  SiS  +  £e. 

3.  2  CaO  +  FeS  +  SiS  =  2  CaS  +  SiO2  +  Fe. 

The  SiS  in  all  these  equations  is  thought  of  as  being  pro- 
duced by 

Si  +  FeS  =  SiS  +  Fe. 

Also  they  all  represent  the  same  reaction,  namely: 

2  CaO  +  2  FeS  +  Si  =  2  CaS  +  SiO2  +  2  Fe. 
The  slag  will  be  made  thinly  liquid  by  the  silica  produced 
and,  in  this  reaction,  i  sulphur  requires  K  silicon. 
(6)  With  the  use  of  fluor-spar, 

1.  2  "CaF2  +  SiS  +  FeS  =  2  CaS  +  SiF4  +  Fe. 

The  SiS  is  produced  by  the  equation  FeS  +  Si  =  Fe+SiS. 

2.  2  CaF2  +  2  SiS  =  2  CaS  +  SiF4  +  Si. 
The  Si  would  decompose  more  FeS. 


406  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

Both  reactions  therefore  mean  the  same,  namely: 
2  CaF2  +  2  FeS  +  Si  =  2  CaS  +  SiF4  +  2  Fe. 
The  slag  will  become  more  basic,  that  is  thicker,  and  by  this 
reaction  also  i  sulphur  requires  ]/z  silicon. 
Resume  of  the  equations. 

(a)  2  CaO  +  2  FeS  +  Si  =  2  CaS  +  Si02  +  2  Fe. 

(b)  2  CaF2  +  2  FeS  +  Si  =  2  CaS  +  SiF4  +  2  Fe. 

The  reactions  are  the  same  except  that  in  one  the  oxide,  in 
the  other  the  fluoride,  is  the  reagent;  and  by  both  processes  the 
same  amount  of  silicon  is  necessary. 

Desulphurization  by  the  alternate  reaction  between  FeO 
and  FeS  and  the  formation  of  S02  cannot  be  carried  out  with 
fluid  metal  to  complete  success,  and  for  this  reason  it  is  only 
suitable  for  such  cases  where  complete  desulphurizaion  is  not 
necessary. 

Silicon. — The  good  influence  of  a  certain  silicon  content  in 
gray  pig  iron  and  gray  iron  castings  is  well  known.  To  a  certain 
degree  too  high  silicon  in  the  pig  iron  is  a  disadvantage  for  gray 
iron  castings,  particularly  for  the  larger  ones,  as  it  brings  about 
a  coarsely  crystalline  structure,  and  therefore  makes  weaker 
castings.  On  the  other  hand  the  silicon  in  iron  or  steel  can 
easily  be  raised  by  the  addition  of  ferro-silicon  to  the  molten 
bath. 

Silicon  can  be  removed  from  molten  iron  and  steel  by  oxida- 
tion, as  well  by  means  of  ore  as  by  the  oxygen  of  the  air,  a  process 
that  naturally  takes  place  more  easily  on  a  basic  than  on  an  acid 
hearth.  The  silicon  burns  before  the  carbon  if  the  temperature 
is  low,  at  higher  temperatures  it  is  only  removed  completely 
when  the  carbon  is  already  partly  oxidized,  while  at  high  tem- 
peratures the  silica  in  the  slag  is  again  reduced  by  the  carbon  in 
the  bath. 

Copper  and  Arsenic. — Neither  of  these  elements  can  be 
removed  economically  at  present  from  the  bath,  so  that  if  a 
certain  copper  and  arsenic  content  is  required  in  the  finished 
material,  an  appropriate  mixture  must  be  charged. 

Carbon. — The  carbon  can  be  removed  from  the  bath  by  the 


THE   ELECTRO-METALLURGY   OF   IRON   AND   STEEL  407 

oxygen  of  the  ore  or  by  that  of  the  air,  with  the  formation  of 
carbon-monoxide.  If  the  refining  is  carried  out  by  means  of 
ore,  then  iron  is  reduced,  a  process  that  requires  heat.  It  is 
probable  that  the  metal  may  dissolve  a  certain  amount  of  carbon- 
monoxide,  for  iron  heated  in  a  stream  of  nitrogen  shows  a  melting 
point  of  1506°  C.,  but  when  heated  in  a  stream  of  carbon-mon- 
oxide only  1406°  C.,  a  phenomenon  that  is  explained  by  the 
assumption  that  carbon-monoxide  alloys,  at  least  partially, 
with  iron.  On  the  other  hand  low  carbon  steel  baths  easily 
take  up  carbon  whether  the  latter  is  added  in  a  solid,  liquid,  or 
gaseous  condition,  either  in  the  elementary  form  or  as  carbon 
containing  alloys  such  as  ferro-manganese,  etc. 

Oxygen. — Oxygen  may  occur  in  steel  combined  with  other 
elements,  for  example,  as  CaO,  SiO2,  MnO,  A12O3,  etc. 
These  oxides  are  only  mechanically  mixed,  not  alloyed  with  the 
steel,  and  they  are  usually  classed  as  "inclusions."  Such  in- 
clusions are  undesirable  in  high  quality  steels  for  they  loosen  the 
structure,  and  so  lower  the  physical  properties.  In  addition  to 
this,  however,  steel  can  contain  oxygen  in  the  form  of  ferrous 
oxide,  and  such  a  constituent  is  especially  to  be  feared  for  it 
alloys  with  the  metal,  and.  like  sulphur,  brings  about  red  short- 
ness. 

It  is  possible  to  remove  this  ferrous  oxide  from  the  metal  by 
chemical  means,  reducing  it  by  other  elements  according  to  the 
equation: 

FeO  +  X  =  XO  +  Fe. 

Elements  that  can  serve  as  reducing  agents  for  ferrous  oxide 
must  answer  the  following  requirements: 

(1)  They  should  not  bring  about  any  development  of  gases 
in  the  reduction,  for  then  the  metal  does  not  cast  quietly,  and 
opportunity  is  given  for  the  formation  of  gas  inclusions.     There- 
fore reduction  by  means  of  carbon  or  carbides,  electrodes,  etc., 
is  bad,  because  the  formation  of  carbon-monoxide  is  the  result. 

(2)  They    must    have    a    high    volatilization    temperature. 
Therefore  the  alkali  metals  are  bad  to  use,  for  they  escape  from 
the  bath  for  the  most  part  as  gas  without  bringing  about  reduc- 


408  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

tion.  This  is  altogether  apart  from  their  strong  attack  on  the 
brickwork. 

(3)  They  must  easily  reduce  the  ferrous  oxide,  and  for  this  it 
is  necessary  that  the  metal  should  dissolve  in  the  bath.     In  this 
way  only  is  a  complete  contact  and  reaction  possible. 

(4)  They  must  easily  slag  off,  and  separate  from  the  metal. 
Manganese,  silicon,  aluminum,  etc.,  are  generally  used  as 

reducing  agents,  and,  recently,  for  producing  high  quality  steels, 
certain  alloys  of  silicon  with  calcium,  magnesium,  manganese, 
and  aluminum.  At  the  same  time  vanadium  and  titanium  should 
be  mentioned,  for  their  influence  ought  to  be,  in  the  first  place, 
very  strongly  reducing  on  the  last  traces  of  ferrous  oxide. 

For  ordinary  purposes  ferro-manganese  is  mostly  used  for 
deoxidation.  Its  reaction  with  ferrous  oxide,  however,  only 
takes  place  very  slowly,  and  if  the  deoxidation  is  to  be  moderately 
satisfactory  a  considerable  excess  of  manganese  must  be  added 
to  the  bath.  For  this  reason  only  high  manganese  material  can 
be  produced  which  is  not  applicable  as  high  quality  steel  for 
different  purposes.  The  slow  influence  of  the  ferro-manganese 
is  caused  by  the  alloy  having  to  become  dissolved  before  it  can 
alloy  with  the  metal.  Solid  manganese  must  first  melt  in  the 
bath  before  it  can  carry  out  its  deoxidizing  action.  Because  of  this 
the  deoxidation  process  would  be  accelerated  if  liquid  ferro-manga- 
nese were  added,  and  by  using  this  method  the  amount  necessary  can 
be  considerably  reduced,  as  the  loss  of  manganese  in  the  shorter  time 
is  smaller.  In  the  electric  furnace,  where  the  ferro-manganese 
works  in  a  neutral  atmosphere,  the  minimum  amount  can  natu- 
rally be  used  for  deoxidation,  because  the  alloy  has  opportunity 
to  react  on  the  bath  for  a  long  time  without  danger  of  being 
burnt  by  hot  gases.  Also  the  necessary  excess  of  manganese  in 
the  bath  can  be  lowered,  as  the  manganese  can  work  on  the 
bath  without  trouble.  A  disadvantage  of  this  method  of  de- 
oxidizing by  means  of  ferro-manganese  is  that,  with  the  neces- 
sarily large  amount  of  alloy  used,  the  carbon  which  is  unavoid- 
ably present  in  the  blast  furnace  alloy  also  takes  a  part  in  the  re- 
action. It  follows  that  the  bath  should  be  allowed  to  stand  for 
a  long  time  after  the  ferro-manganese  addition  in  order  to  allow 


THE    ELECTRO-METALLURGY   OF  IRON  AND   STEEL  4Q9 

the  gas  to  escape.  This  gas  removal  is,  however,  only  complete 
if  the  bath  has  been  given  some  opportunity  to  take  up  silicon. 
Unfortunately,  there  is  no  clear  explanation  for  the  influence  of 
the  silicon.  It  either  reduces  the  carbon-monoxide  dissolved 
in  the  bath,  or  else  it  makes  the  metal  able  to  unite  with  the 
gases,  especially  the  carbon-monoxide.  The  latter  view  is  the 
more  probable,  for  it  has  been  mentioned  that  iron  has  a  very 
low  melting  point  when  exposed  to  heat  in  an  atmosphere  of 
carbon-monoxide,  which  is  easily  explained  by  the  theory  of 
the  existence  of  an  iron-carbon-monoxide  alloy. 

Silicon  is  moreover  a  very  strongly  deoxidizing  material,  and 
scarcely  more  has  to  be  used  than  the  amount  theoretically 
necessary.  The  silica  easily  goes  into  the  slag,  and  there  is  no 
production  of  gas,  as  the  small  amount  of  ferro-silicon  used  adds 
practically  no  carbon.  Heats  deoxidized  by  means  of  silicon 
can  be  cast  quietly  and  easily  for  the  reasons  just  mentioned. 

Aluminum  is  also  an  effective  reducing  agent,  but  there  is 
the  disadvantage  that  alumina  is  produced  which,  on  account 
of  its  high  melting  point,  does  not  slag  off  completely  and  some 
remains  as  a  fine  net-work  in  the  metal,  lowering  the  physical 
properties  of  the  latter.  In  the  production  of  high  quality 
material  the  use  of  aluminum  is  therefore  not  to  be  recommended, 
above  everything  no  aluminum  should  be  used  while  pouring 
into  the  moulds,  for  then  much  less  heat  is  present  for  melting 
the  alumina  than  in  the  furnace. 

Recently  alloys  of  vanadium  and  titanium  have  been  recom- 
mended, the  latter  produced  by  the  Goldschmidt  reaction. 
They  are  very  effective,  but  at  present  their  high  price  limits 
their  use.  It  may  be,  however,  that  the  price  of  vanadium  will 
be  lowered  when  the  alloy  can  be  produced  in  the  electric  furnace, 
but  due  to  the  formation  of  carbides  special  attention  must  be 
paid  to  the  making  of  a  low  carbon  vanadium  alloy. 

Deoxidation  requires  that  during  the  whole  process  there 
should  be  a  purely  neutral  or  reducing  atmosphere.  Formerly 
this  condition  was  only  obtained  in  the  graphite  crucible,  silicon 
being  reduced  from  the  crucible  walls  by  carbon,  and  forming 
the  reducing  agent.  For  this  reason  crucible  steels  made  from 


410   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

a  pure  charge  were,  up  to  the  present  time,  the  best  obtainable, 
although  low  silicon  material  was  only  produced  with  very  great 
difficulty  because  of  the  silicon  reduced  from  the  acid  crucible 
walls.  The  melting  of  low  silicon  crucible  steels  had  to  be  done, 
therefore,  in  costly  alumina  crucibles. 

FLUXES,  FERRO  ALLOYS,  ETC.,  USED  IN  THE  ELECTRIC 
FURNACE 

(1)  Ferro-manganese. — For  reasons  of  economy  the  ordinary 
blast  furnace  product  is  used  with  the  average  analysis — 

Manganese 80 . 00% 

Silicon 1 . 20% 

Phosphorus 0.25% 

Carbon 6.00% 

The  rather  high  phosphorus  content  can  be  neglected,  for  only 
a  small  percentage  of  ferro-manganese  is  used  so  that  the  phos- 
phorus of  the  charge  is  practically  not  increased.  Occasionally, 
pure  manganese,  which  is  naturally  very  expensive,  is  used  for 
special  purposes. 

(2)  Ferro-chromium. — Here  also  the  cheap  high  carbon  mate- 
rial is  usually  good  enough,  with  the  analysis — 

Chromium 64% 

Carbon 8-9% 

especially  when  the  alloy  is  added  liquid.  The  carbon  does  not 
produce  any  gas,  for  the  alloy  is  only  added  after  the  bath  is 
deoxidized.  Of  course  the  carbon  of  the  alloy  must  be  consid- 
ered in  figuring  the  carbon  of  the  steel.  The  more  expensive 
low  carbon  alloys  are,  however,  used  in  many  cases. 

(3)  Ferro-silicon. — The  best  is  the  ordinary  50  per  cent,  elec- 
tric furnace  grade.    High  silicon  blast  furnace  pig  irons  can 
indeed  be  used,  especially  with  such  a  market  as  the  present,  but 
the  carbon  of  this  grade  of  material  is  higher  than  desirable. 
In  making  high  silicon  steels,  such  as  dynamo  plates,  etc.,  the 
90  per  cent,  alloy  is  used. 

(4)  Lime. — This  should,  of  course,  be  as  free  from  sulphur  and 
phosphorus  as  possible.    In  burning  the  lime  it  should  be  par- 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  4H 

ticularly  remembered  that  with  the  use  of  high  sulphfir  fuel, 
such  as  is  generally  employed,  the  lime  takes  up  considerable 
sulphur,  so  that  with  large  pieces  of  lime  the  sulphur  is  highest 
at  the  outside  and  decreases  towards  the  centre. 

Analyses  I  II 

Outer  shell o.so%S       0.48%  S 

Middle  part 0.21%  S       0.20%  S 

Core o.os%S       0.06%  S 

One  is  therefore  bound  to  consider  the  use  of  raw  limestone, 
especially  for  the  formation  of  the  refining  slag.  As  lime  free 
from  sulphur  is  needed,  the  stone  could  be  burned  in  a  shaft  or 
rotating  furnace  by  means  of  waste  gases,  so  far  as  they  are 
available.  Moreover,  tests  with  the  ring  furnace  have  shown 
that  the  lime  in  a  chamber  does  not  show  the  same  increase  in 
sulphur  at  all  parts  of  the  chamber.  An  example  is  given  below. 

The  raw  limestone  used  was  very  uniform  and  had  0.05%  S. 
Tests  taken  from  the  material  after  being  burnt  showed  the 
following  results: 

Average  test  from  the  wall  of  the  chamber o.n%S 

"  "    in  front  of  the  fire o.  16%  S 

"          "    somewhat  further  from  the  fire o.  16%  S 

"          "    at  the  door 0.09%  S 

As  lime  burnt  in  the  ring  furnace  is  mostly  used  for  other 
purposes,  one  is  in  the  position  to  take  the  low  sulphur  part  and 
use  it  specially.  If  burnt  lime  is  bought  it  is  welPto  consider 
the  percentage  of  moisture  and  carbon-dioxide  contained.  On 
the  other  hand  a  small  proportion  of  carbon-dioxide  is  not  a 
great  disadvantage  to  the  process,  for  the  slag  must  finally 
show  a  certain  amount  of  carbon-dioxide,  at  least  for  desulphur- 
izing and  deoxidizing.  Also  certain  percentages  of  magnesia  in 
the  lime  are  a  disadvantage  as  it  makes  the  slag  less  fusible. 

(5)  Fluor-Spar—  This  should  be  as  low  as  possible  in  sulphur 
and  phosphorus,  and  is  suitably  paid  for  according  to  its  contents 
of  fluorine.     Also  contained  magnesia  is  a  disadvantage. 

(6)  Iron  Ore  for  the  Carbon  Refining  Process.— Any  ore,  even 
brown  iron  ore,  can  be  used  but  high  percentage  ore  is  recom- 


412  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


mended,  so  that  the  slag  volume  and  the  heat  lost  in  the  slag 
are  not  too  great.  Naturally,  it  is  also  better  to  use  ore  not 
too  high  in  sulphur,  especially  if  metal  has  to  be  worked  that  is 
high  in  carbon,  sulphur,  and  phosphorus.  Phosphorus  in  the 
ore,  on  the  other  hand,  is  not  harmful  so  that  minette  ore  can  be 
used,  for  the  bath  cannot  reduce  phosphoric  acid  from  the  ore. 
(7)  Carbon. — A  material  should  be  chosen  that  is  low  in  ash, 
sulphur,  and  volatile  matter.  Graphite,  anthracite,  petroleum, 
coke,  etc.,  can  be  used  according  to  one's  wish  and  the  market 
price.  Below  are  given  several  analyses  of  these  materials: 


Vol.  matter 

Ash 

Sul. 

Petroleum  coke  

3-5% 

o,7% 

1-2% 

Retort  carbon  

0.6 

'    1.8 

1.2 

Flake  graphite  

1.3 

6.9 

O.5 

They  are  best  used  in  moderate  sized  pieces.  If  finely 
divided  material  must  be  used  it  is  best  to  weigh  it  out  into 
bags,  or  -else  briquette  it. 

THE  ELECTRIC  FURNACE  AS  A  MELTING  FURNACE  FOR  IRON  AND 
STEEL,  AND  IRON  ALLOYS  OF  EVERY  KIND 

The  advantages  of  melting  in  the  electric  furnace  are  chiefly 
brought  about  by  the  possibility  of  maintaining  purely  neutral 
or  reducing  atmospheres,  which  means  that  the  hot  materials 
do  not  attack  the  furnace  walls  as  in  the  cupola,  air  furnace,  etc. 
As  is  well  known  the  melting  of  pig  iron,  etc.,  in  the  cupola 
is  attended  with  a  considerable  absorption  of  sulphur,  which 
sensibly  affects  the  final  quality.  For  instance: 

C%         Si%        Mn%       S% 

Material  before  melting  3.50         2.90         1.20        0.035 

After  melting  once 3. 40        2.70         i.io        0.055 

After  melting  twice 3.30         2.50         0.80         0.073 

Foundries  making  low  sulphur  material  such  as  high  quality 
castings,  malleable  iron  castings,  etc.,  must  therefore  melt  either 
in  the  open  hearth  or  air  furnace,  and  notwithstanding  this  most 
expensive  operation  the  undesirable  action  of  the  furnace  gases 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL  413 

on  the  charge  is  not  prevented,  as  is  shown  by  the  following 

analyses: 

A .  Melting  of  Pig  Iron: 

C%  Si%  Mn%  S%  P% 

(1)  Before  melting 3.30  1.55  1.67  0.053  0.36 

Finished  material 3.25  0.66  0.76  0.083  0.37 

(2)  Before  melting 3.18  0.59  1.79  0.075  0.27 

Finished  material  3.16  0.22  1.22  0.093  0.27 

(3)  Before  melting 3.06  0.72  1.98  0.069  0.23 

Finished  material 3.02  0.28  0.28  0.090  0.23 

The  melting  in  all  these  cases  took  place  in  an  air  furnace, 
using  bituminous  coal  with  about  0.7%  sulphur. 

B.  Steel  Castings  Melted  in  a  $-Ton  Open  Hearth  Furnace. 

C  s 

(1)  Before  melting 0.050 

Finished  material o .  30  o .  060 

(2)  Before  melting o .  037 

Finished  material 0.25  o. 050 

(3)  Before  melting o .  048 

Finished  material 0.45  0.062 

Naturally  those  plants  suffer  which  have  to  use,  anyhow, 
high  sulphur  pig  iron  and  fuel;  on  the  other  hand,  with  melting 
in  the  electric  furnace  there  is  no  oxidation  of  the  iron  nor  of  the 
valuable  constituents  silicon,  manganese,  etc.,  such  as  is  shown 
in  the  above  analyses.  As  is  well  known  in  the  melting  of  an 
ordinary  foundry  iron,  a  loss  of  at  least  10%  of  the  silicon  is 
calculated,  with  higher  silicon  irons  still  more,  and  on  this 
account  less  scrap  can  be  melted  than  the  silicon  of  the  cold 
foundry  iron  would  allow.  In  electric  furnace  melting  there  is 
no  loss  of  iron,  nor  metal  loss  in  the  slag,  for  no  melting  slag  is 
necessary. 

Electric  melting  is  particularly  important  in  the  production 
of  hard  castings.  The  high  manganese  pig  iron  used  suffers  a 
high  loss  of  manganese  in  melting  in  the  ordinary  furnace,  which 
is  entirely  absent  with  electric  melting,  so  that  the  amount  of  the 
expensive  high  manganese  iron  necessary  can  be  considerably 
lowered.  An  important  point  that  recommends  the  electric 


414     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

melting  of  iron  for  foundry  purposes  is  that  in  the  electric  furnace 
the  temperature  can  be  governed  as  desired.  The  percentage 
of  bad  castings  therefore  ought  to  be  somewhat  reduced,  for  the 
casting  of  cold  iron,  which  may  happen  with  the  cupola  even 
with  the  most  careful  supervision  of  the  operation,  is  excluded. 
Also  in  regard  to  the  quality  of  the  castings,  electric  melting 
should  bring  about  considerable  improvement,  apart  from  the 
avoidance  of  an  increase  in  sulphur,  especially  for  pipe  and  thin- 
walled  castings,  for  which  high  phosphorous  brittle  material  has 
now  to  be  used  in  order  to  fill  out  the  moulds.  As  it  is  possible 
to  increase  the  temperature  of  a  low  phosphorous  iron  in  the 
electric  furnace  to  such  an  extent  that  the  same  fluidity  is  pro- 
duced as  with  a  high  phosphorous  iron,  one  can,  therefore,  under 
these  conditions,  produce  thin-walled  castings  from  low  phos- 
phorous iron  which  is  not  brittle,  without  getting  porous  or 
blowhole  castings. 

The  electric  furnace  is  also  very  suitable  for  melting  ferro- 
manganese,  and  all  the  ferro  alloys,  which  are  so  much  used  in 
steel  plants  and  also  recently  in  foundries.  Every  metallurgist 
knows  that  for  quickly  completing  heats  of  steel  in  the  furnace 
or  in  the  ladle,  considerably  more  ferro-manganese  must  be  used 
if  it  is  added  cold  than  if  added  liquid.  In  spite  of  this,  up  to 
now,  he  has  been  forced  to  be  satisfied  with  the  use  of  solid  pre- 
heated ferro-manganese,  because  the  metallurgical  furnaces  avail- 
able for  melting  this  easily  oxidizable  material  are  not  practical 
as  the  loss  increases  immeasurably.  The  electric  furnace  is  here 
particularly  applicable,  for  with  a  reducing  atmosphere  an  oxida- 
tion of  the  manganese  is  excluded.  Harden1  reports  saving  44.3% 
ferro-manganese  when  poured  in  its  molten  state  from  an  elec- 
tric into  steel,  instead  of  using  cold  lumps;  total  melting  and 
holding  cost  about  $12  per  ton.  The  finished  material  is  also 
superior,  being  free  from  "ghost  lines"  and  hard  lenses.  The 
introduction  of  the  electric  furnace  into  foundries,  steel  works, 
etc.,  will  be  further  favored  by  the  fact  that  during  the  melt- 
ing an  excellent  mixing  of  the  charge  will  take  place.  Until  now 

'John  Harden,  1917,  "Fifth  General  Meeting  of    Chemists,"   Stockholm, 
Sweden;  see  also  Iron  Age,  April  n,  1918,  for  digest. 


THE   ELECTRO-METALLURGY   OF   IRON   AND   STEEL          415 

in  cupola  melting  one  is  compelled  to  take  the  metal  more  or 
less  as  it  comes,  even  when  making  a  special  material,  because, 
though  one  may  know  the  composition  of  the  material  charged, 
it  is  difficult  to  figure  on  the  loss  during  melting,  and  therefore 
on  the  final  composition.  With  the  electric  furnace,  on  the  other 
hand,  where  there  is  no  oxidation,  one  can  calculate  exactly 
beforehand  the  composition  of  the  final  fluid  metal,  apart  from 
the  fact  that  an  absolutely  uniform  material,  free  from  impuri- 
ties, will  be  produced.  Bad  heats,  because  of  low  or  high  sili- 
con, will  be  excluded  because  one  can  add  to  the  bath  the  right 
amount  of  ferro-silicon  on  the  one  hand,  or  low  silicon  pig  on  the 
other. 

Attempts  have  often  been  made  previously  to  increase  the 
silicon  in  a  low  silicon  iron  by  the  addition  of  ferro-silicon 
to  the  casting  ladle,  a  process  that  is  only  partially  successful, 
for,  to  absorb  the  silicon,  it  must  be  first  melted,  which  requires 
a  very  hot  bath  of  metal  and  also  a  certain  amount  of  time. 
Both  conditions  are  fully  met  in  the  electric  furnace,  but  not 
in  the  casting  ladle 

Also  cast-iron  scrap,  turnings,  etc.,  can  be  melted  without 
the  scrap  being  for  the  most  part  burned  and  slagged  off  as  in 
the  cupola.  Indeed,  this  great  loss,  when  melting  fine  material 
such  as  turnings,  etc.,  in  the  cupola,  has  forced  those  plants 
which  have  considerable  amounts  of  such  scrap  to  briquette 
it  before  melting.  The  considerable  cost  of  this  process  is 
always  lower  than  the  saving  due  to  the  decreased  loss. 
Also,  a  low  carbon  material,  similar  to  cold-blast  iron,  can 
be  produced  without  difficulty  by  the  melting  in  of  wrought- 
iron  scrap. 

The  melting  of  pig  iron  in  the  electric  furnace  can,  at  the 
same  time,  be  combined  with  a  refining  of  sulphur  or  silicon. 
In  regard  to  the  sulphur  its  removal  is  easy  if  a  lime  slag  is  pro- 
duced. As"  the  silicon  content  of  the  pig  iron  is  almost  always 
high  enough,  desulphurization  readily  takes  place  according 
to  the  equations  given  before,  if  there  is  temperature  enough. 
The  sulphur  enters  the  slag,  which  is  drawn  off.  Such 
desulphurized  iron  is  particularly  suitable  for  malleable  iron 


416     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

castings,  so  that  even  for  this  high-grade  material  a  cheap 
high  sulphur  iron  or  scrap  can  be  used.  The  lowering  of 
the  silicon  will  naturally  be  brought  about  by  the  addition  of 
a  correspondingly  low  silicon  iron. 

DUPLEXING  WITH  THE  CUPOLA 

Elliott1  mentions  his  two  years'  experience  making  not  only 
gray  iron  but  also  malleable  iron  for  castings.  Editorially,  the 
Iron  Age,1  in  discussing  the  results,  says,  "The  changes  in  the 
metal  are  striking,  when  it  is  considered  that  the  iron  is  kept 
under  electric  conditions  less  than  half  an  hour.  Besides  the 
greater  fluidity  and  a  certain  amount  of  refining,  espe- 
cially as  to  sulphur,  the  density  of  the  metal  has  been  in- 
creased, the  structure  changed  and  the  strength  augmented 
75  to  90%." 

Moldenke,  in  discussing  this,  pointed  out  that  this  process 
affords  a  solution  of  the  sulphur  problem  in  cast-iron  scrap. 

In  discussing  this  in  detail,  Elliott  goes  on  to  say  that  the 
electric  furnace  has  now  been  making  a  super  grade  of  gray 
iron  castings  due  to  the  insistent  demand  for  physical  prop- 
erties of  a  higher  order  than  are  commonly  characteristic  of 
such  iron. 

This  experience  covers  mostly  gray  iron  for  steam-valve 
bodies,  except  as  otherwise  noted.  However,  similar  is  the  case 
of  cylinders  for  locomotives  using  superheated  steam,  and  those 
for  internal  combustion  cylinders. 

The  two  prime  qualities  most  generally  wanted  in  high-grade 
iron  are  strength  and  solidity.  The  best  strength  gray  iron 
shows  is  under  compression,  and  its  worst  is  under  impact 
and  vibration;  between  comes  transverse  strains  and  tension. 
Where  unusual  strength  of  iron  is  required  it  is  usually  sub- 
jected to  either  impact,  vibration,  or  tension,  or  where  cast 
iron  is  at  its  greatest  disadvantage.  Under  solidity  may  be 
included  a  number  of  related  items  such  as  density,  closeness 
of  grain,  and  freedom  from  subcutaneous  imperfections,  such  as 

'See  A.  E.  S.,  April,  1919;  also  Iron  Age,  April  10,  1919. 


THE    ELECTRO-METALLURGY    OF    IRON   AND    STEEL  417 

slag  inclusions,  graphite  segregation,  blow-holes  and  shrink- 
holes. 

Strong  irons  without  exception  require  high  pouring  tempera- 
tures, because  they  have  high  melting  points  and  minimum 
fluidity.  The  irons  most  easily  melted,  and  consequently  the 
most  fluid  ones,  have  a  high  percentage  of  phosphorus  in  their 
make  up.  Medium  and  high  phosphorous  irons  comprise  by 
far  the  greatest  part  of  the  melt  of  the  gray  iron  foundries. 
These  are  the  popular  casting  irons,  and  it  is  well  known  that 
phosphorus  has  done  as  much  or  even  more  than  any  other 
element  to  popularize  gray  iron  for  castings.  Still,  phosphorus 
has  the  grave  fault  of  unfavorably  affecting  the  strength  of 
iron,  a  thing  it  accomplishes  by  forming  in  the  iron  mass  a  net- 
work of  structurally  free  phosphide,  which  is  quite  brittle. 
Although  easily  fluid,  high  phosphorous  irons  are  brittle  and 
generally  lacking  in  strength.  Conversely,  tenacious  strong  irons 
are  necessarily  low  in  phosphorus.  The  fact  that  strength  and 
fluidity  do  not  go  hand-in-hand  brings  to  light  the  greatest 
defect  of  the  cupola,  namely,  its  thermal  limitations.  The 
melting  operation  in  any  furnace  is  divided  into  preheating, 
melting,  and  superheating.  For  the  first  two  the  cupola  is 
preeminent,  but  for  superheating  the  cupola  has  not  the  same 
excellence. 

All  ordinary  grades  of  gray  iron,  those  with  medium  and 
high  percentages  of  phosphorus,  cannot  be  melted  more  easily 
or  more  economically  than  in  the  cupola.  For  melting  efficiency 
this  furnace  takes  precedence  over  the  reverberatory  or  air  fur- 
nace and  the  regenerative  type  open-hearth  (Siemens-Martin) 
furnace. 

From  the  standpoint  of  process  alone,  the  cupola  is  blame- 
less, but  from  the  high  ground  of  product,  it  shows  seri- 
ous faults.  The  two  worst  of  these  are  its  weakness  as  a 
superheater  for  molten  iron,  and  its  incapacity  as  a  re- 
finer. The  cupola  is  not  a  refining  furnace,  and  sometimes  the 
hottest  possible  iron  is  not  hot  enough  for  the  best  casting 
results. 

With  extreme  solidity  exacted  and  for  really  alluring  possi- 


418    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

bilities  and  extraordinary  eastings,  the  resulting  basic  electric 
furnace  is  the  one  to  duplex  with  the  cupola. 

The  question  arises  why  is  the  basic  hearth  preferred?  If 
superheating  only  is  desired,  it  is  entirely  probable  that  the 
acid  furnace  should  be  given  preference;  but  if  an  important 
amount  of  refining  is  advantageous  the  basic  furnace  should  be 
used.  It  is  true  that  the  acid  electric  furnace  exerts  a  con- 
siderably refining  influence  by  virtue  of  the  reducing  condition 
so  readily  maintained  in  it.  On  the  other  hand,  the  refining 
tendency  of  the  basic  furnace  is  so  much  more  pronounced  and 
so  readily  responding  that  the  iron  charge  is  refined  at  the  same 
time  it  is  being  superheated.  By  the  time  the  charge  has  reached 
its  pouring  temperature  it  has  also  reached. a  highly  refined 
condition.  Among  other  results,  the  sulphur  has  been  reduced 
very  materially,  provided  the  proper  basic  and  reducing  slag  has 
been  maintained. 

Sulphur  in  cast  iron  has  so  long  been  considered  a  neces- 
sary evil  that  its  presence  not  only  is  commonly  con- 
doned, but  occasionally  is  credited  with  certain  benefits.  No 
doubt  there  are  a  few  of  these  last,  for  instance,  where  it 
aids  in  producing  chill.  But  in  general  there  is  good  reason 
to  believe  that  iron  is  much  better  for  its  absence.  That  it 
induces  unsoundness,  when  in  excess,  is  general  knowledge; 
and  sluggishness  of  metal  is  a  closely  allied  evil  that  travels 
in  the  train  of  sulphur  and  works  unfavorably  to  solid 
castings. 

A  medium  or  high  sulphur  content  is  inevitable  in  the  prod- 
uct of  the  cupola  furnace,  which  in  the  basic  electric  is  prac- 
tically eliminated  as  a  matter  of  course.  The  basic  electric  fur- 
nace removes  most  of  the  sulphur  while  the  metal  is  being 
superheated.  This  reaction  gives  the  electric  certain  obvious 
compensating  economies  in  the  choice  of  raw  materials  used  in 
the  cupola  phase  of  the  process.  Iron  coming  from  the  cupola 
with  0.100%  sulphur,  after  undergoing  25  minutes'  treatment  in 
the  basic  electric,  generally  contains  about  0.03%  sulphur. 
Heats  have  been  made  reducing  sulphur  from  0.099  to  0.022% 
and  from  0.088  to  0.018%.  This  possibility  of  so  low  a  sulphur 


THE   ELECTRO-METALLURGY    OF   IRON   AND   STEEL          419 

in  gray  iron  castings  opens  up   a   new  field  for  metallurgical 
investigations. 

Carbon  regulation  is  possible  to  a  most  useful  extent  in  the 
electric  furnace,  total  as  well  as  combined  and  graphitic.  By 
placing  steel  scrap  in  the  furnace  before  adding  the  molten 
iron  from  the  cupola,  total  carbon  can  with  accuracy  be  reduced 
to  any  desired  amount. 

Uniformness  among  different  heats,  homogeneity  in  the  indi- 
vidual heat,  close  carbon  regulation,  and  unlimited  temperature 
are  a  quartet  of  benefits  of  the  electric  furnace  not  found  in  any 
other  furnace.  This  enables  any  compositon  and  exceptional 
quality  to  be  made,  many  of  which  are  so  often  claimed  and 
so  rarely  reached  by  the  cupola  alone,  and  the  cupola  product 
of  which  goes  under  many  hybrid  names. 

Also  correctly  balancing  of  the  combined  and  uncombined 
carbons  is  a  matter  of  no  great  intricacy  in  the  electric,  by 
varying  the  silicon  content.  In  short,  the  capriciousness  of  the 
cupola,  with  reference  to  carbon  control,  is  replaced  in  the 
electric  by  substantial  certainties. 

The  well-known  advantages  of  making  manganese  and  other 
similar  additions  with  these  mixtures  are  here  also,  and  the 
manganese  losses  are  nil.  The  one  outstanding  advantage  from 
the  standpoint  of  composition  is  the  absolute  control  of  the  mix- 
ture, making  duplication  of  results  more  a  matter  of  correct 
calculation,  and  less  the  effect  of  happy  accident. 

A  concrete  example  of  results  actually  obtained  in  every-day 
running  practice  is  as  follows: 

A  rather  ordinary  mixture  of  pig  iron  and  foundry  scrap 
was  melted  as  usual  in  the  cupola,  transferred  to  a  basic  electric, 
and  there  superheated  and  refined  under  a  lime  slag. 

The  untreated  iron  was  of  a  composition  regularly  giving 
a  standard  "  arbitration  "  test  of  bars  that  broke  under  an  average 
transverse  load  of  1,350  kg.  (2,950  Ibs.)  with  a  deflection  of 
25  mm.  (.10  inch).  After  treatment  in  the  electric  furnace, 
the  iron  gave  the  same  kind  of  bars  breaking  at  slightly  over 
2,000  kg.  (4,400  Ibs.)  and  at  a  deflection  of  2.9  mm.  (.115 
inch).  The  specific  gravity  was  increased  from  7.10  to  7.25. 


420     ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

About  25  minutes  was  the  time  of  electric  furnace  treatment, 
and  the  current  consumption  was  114  kw.  hrs.  per  metric  ton 
(2,204  Iks.). 

Broadly  speaking,  duplexing  with  the  cupola  is  feasible;  first, 
for  castings  having  an  exact  unusual  tenacity,  solidity,  and 
other  physical  properties;  secondly,  there  are  those  castings,  dif- 
ficult to  run  on  account  of  having  thin  sections  and  relatively 
large  sizes;  thirdly,  those  of  high  quality  whose  extreme  foundry 
cost  is  but  a  small  part  of  the  total  cost  of  the  finished 
article. 

For  the  moment,  leaving  the  cupola,  attention  is  again  called 
to  the  advantage  of  using  the  electric  in  connection  with  the 
direct  metal  from  the  blast  furnace,  the  electric  furnace  filling 
the  triple  role  of  mixer,  superheater,  and  refiner.  Such  process 
would  make  high-class  gray  iron  castings,  almost  direct  from 
the  blast  furnace,  at  a  cost  very  little  higher  if  any,  and  perhaps 
lower,  than  those  of  the  ordinary  cupola. 

THE  ELECTRIC   MALLEABLE  CASTING 

White  iron  for  malleable  castings  may  be  prepared  in  the 
electric  furnace  in  two,  or  possibly  more,  different  ways  econom- 
ically. In  foundries  where  the  malleable  department  is  only  a 
small  annex  requiring  but  a  few  tons  of  castings  each  day,  the 
best  method  is  to  melt  down  a  cold  charge  of  suitable  composi- 
tion in  the  electric  to  refine  and  finally  superheat  before  pouring. 
A  great  many  hundreds  of  tons  of  excellent  malleable  castings 
have  been  made  this  way  by  Elliott.  In  foundries  specializing 
in  malleable  and  consequently  running  a  large  daily  tonnage,  it 
would  be  more  economical  and  satisfactory  to  follow  the 
duplexing  process  that  has  been  described  for  electric  gray 
iron.  With  a  basic  electric  the  refining  can  be  made  ex- 
tremely effective,  removing  with  great  ease  most  of  the 
sulphur,  which  enables  the  use  of  higher  sulphur  raw  materials 
than  is  customary,  and  brings  about  thereby  an  economy  by 
no  means  trifling. 

In  addition  to  these  two  processes  there  is  the  Kranz  triplex 


THE   ELECTRIC   METALLURGY   OF   IRON   AND   STEEL        421 

process.  It  includes  the  use  of  the  cupola,  the  side  blow  con- 
verter for  lowering  to  a  certain  part  with  the  cupola  melt,  car- 
bon, silicon,  and  manganese,  and  the  electric  for  refining  the 
mixed  cupola  and  converter  metal. 

Aside  from  the  possible  widening  of  the  field  of  raw  mate- 
rials so  as  to  admit  cheaper  grades  of  iron  and  scrap,  the  elec- 
tric furnace  processes  for  malleable  iron  have  even  greater  bene- 
fits than  are  shown  in  the  product  itself.  Chief  among  these  is 
molten  iron,  hot  enough  not  to  freeze  either  in  the  ladle  before 
being  poured  or  in  the  molds  after  pouring  but  before  the  cast- 
ings are  perfectly  "run." 

The  raw-material  white  iron,  before  being  cast  into  the  molds 
for  malleable  castings,  has  a  temperature  and  time  range  of 
workable  fluidity  that  is  decidedly  narrower  than  has  gray  iron. 
Gray  iron  may  drop  nearly  twice  the  number  of  degrees  in  tem- 
perature before  freezing  as  may  white  iron;  consequently,  the 
time  available  for  handling  white  iron  in  the  effective  fluid  state 
is  only  about  half  that  available  for  gray  iron.  The  practical 
result  of  this  undesirable  characteristic  of  white  iron  is  that  when 
fluid  such  iron  cannot  be  held  in  the  ladle  for  long,  and  the 
mortality  among  small  malleable  castings  as  the  result  of  slug- 
gish metal  is  often  appalling.  There  being  no  limit 'to  the  pos- 
sible temperature  in  the  electric,  the  foundrymen  operating  such 
a  furnace  have  the  pleasing  experience  of  seeing  molten  white 
iron  that  is  capable  of  running  even  the  smallest  and  most  intri- 
cate castings  with  losses  through  dull  metal  reduced  to  the 
practical  irreducible  minimum.  Besides  this,  there  is  the  ad- 
vantage of  refinement,  including  desulphurization  and  deoxida- 
tion,  giving  castings  of  exceptionally  high  quality.  Also,  there 
is  the  well-grounded  idea  that  the  use  of  the  electric  furnace 
may  be  made  to  reduce  the  time  necessary  for  malleableizing, 
partly  through  the  extreme  reduction  of  the  sulphur  and  partly 
for  other  reasons. 

As  a  conclusion  it  may  be  taken  that  the  electric  furnace 
has  found  a  place  in  foundries,  etc.,  for  melting  pig  iron,  ferro 
alloys,  etc. ;  particularly  in  the  production  of  high  quality  mate- 
rial. The  advantages  are  an  absence  of  loss  by  melting  and  in 


422       ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  slag,  the  production  of  the  same  metal  as  calculated  theo- 
retically, the  use  of  cheap  high  sulphur  iron,  and  the  melt- 
ing of  more  cast-iron  scrap.  In  general,  no  furnace  will  be 
preferable  for  these  purposes,  for  the  bath  is  heated  uniformly 
enough  and  there  is  no  electrode  action  on  the  metal  due 
to  the  slag  which  would  cause  a  loss  of  manganese  because  of 
vaporization. 

The  profitable  use  of  the  induction  furnace  in  the  melting  of 
fine  scrap  must  be  particularly  mentioned,  for  there  is  always  a 
bath  of  metal  in  the  furnace.  On  charging  the  cold  scrap 
it  immediately  falls  into  this  bath  and  is  therefore  protected 
from  oxidation.  The  power  consumption  per  metric  ton 
of  steel  scrap  melted  in  this  type  of  furnace  is  about  580 
kw.  hrs.,  an  amount  that  makes  electric  melting  appear  quite 
economical. 

THE  ELECTRIC  FURNACE  AS   A   MIXER 

Most  large  steel  works  that  have  several  blast  furnaces,  as 
well  as  foundries  taking  metal  direct  from  the  blast  furnaces, 
already  have  mixer  plants  either  to  regulate  the  production,  to 
get  a  better  mixture  of  the  different  casts,  or  to  obtain  as  thorough 
prerefining  as  possible.  This  means  a  separation  of  the  sulphur 
brought  about  by  a  part  of  the  sulphur  slagging  off  as  a  sulphide 
of  manganese,  if  there  is  sufficient  manganese  in  the  iron.  The 
size  of  the  mixers  varies  a  great  deal  from  25  to  1,000  tons  and 
more  capacity.  The  small  mixers  are  preferably  used  for  iron 
foundries,  such  as  pipe  foundries,  that  take  direct  metal,  but 
the  prevention  of  cooling  with  the  small  mixers  is  naturally  not 
very  good  so  that  sometimes  heating  is  necessary.  If  refining 
is  desired  in  the  mixer,  then  heating  by  means  of  fuel  is  not  so 
profitable  and  there  is  opportunity  for  the  electrically  heated 
mixer,  which  will  be  similar  to  an  ordinary  electric  furnace  of 
very  large  size. 

Furnaces  of  more  than  30  metric  tons  capacity  have,  how- 
ever, not  yet  been  built,  so  that  in  this  respect  there  has 
been  no  experience.  The  requirement  for  an  electric  mixer  is 
that  the  metal  should  be  held  at  the  right  temperature.  The 


THE  ELECTRIC  METALLURGY  OF  IRON  AND  STEEL    423 

question  should  be  solved  by  an  induction  furnace,  for  here  the 
temperature  can  be  kept  at  any  desired  degree,  and  there  is 
also  certainty  of  an  absolute  uniformity  of  the  whole  metal 
because  of  the  movement  of  the  bath.  In  the  mixer  there 
would  also  be  a  thorough  desulphurization  of  the  metal,  so 
that  the  product  would  undoubtedly  meet  the  most  rigid  re- 
quirements of  quality.  The  electric  arc  furnace  would  also  do 
well  here. 

On  the  other  hand,  if  the  mixer  metal  is  to  be  used  for  steel- 
making,  and  then  subjected  to  subsequent  refining  processes, 
heating  with  ordinary  fuels  would  still  in  most  cases  be  the 
more  economical. 

Further,  here  again  the  known  calculations  give  weight 
on  one  side  or  the  other,  namely,  which  is  the  more  expensive 
under  the  conditions  present,  heating  with  electricity  or  direct 
heating  with  fuel? 

THE  REFINING   OF  PIG  IRON 

The  refining  of  pig  iron  can  be  carried  out  very  well  in  the 
electric  furnace,  and  just  as  well  by  the  oxygen  of  ores  as  by  that 
of  the  air.  In  general,  the  induction  furnace  here  would  also  come 
into  consideration,  for  the  refining  process  can  be  carried  out  in 
the  arc  furnace  without  great  electrode  loss  and  use  of  consid- 
erable refining  material. 

The  iron  could  be  melted  direct  in  the  electric  furnace, 
or  the  liquid  metal  could  be  charged  from  the  blast  fur- 
nace, mixer,  cupola,  open  hearth  or  special  furnaces,  after 
the  liquid  metal  had  been  previously  refined,  that  is,  desul- 
phurized, etc. 

Refining  with  ore  in  the  electric  furnace  is,  however,  expen- 
sive because  the  reduction  of  the  ore  takes  place  slowly,  exactly 
as  in  the  Talbot,  Bertrand-Thiel,  and  other  processes,  so  that  the 
current  consumption  caused  by  radiation  is  too  great.  In  order 
to  accelerate  this  reduction,  and  so  save  electric  energy,  one 
could  consider  charging  the  ore  highly  heated,  if  peat ^ or  some 
other  fuel  not  suitable  for  steel-works  furnace  operation  is  readily 
accessible.  Concerning  the  thermal  advantages  brought  about 


424  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

by  the  use  of  highly  heated  ore,  the  following  approximate  rough 
calculations  give  some  information. 

The  pig  iron  contains  3%  carbon,  and  will  be  refined  by  pure 
magnetite  heated  to  800°  C.  According  to  the  equation: 

232  kg.  Fe3O4  +  48  kg.   C  =  168  kg.  Fe  +  112    kg.    CO, 

the  30  kg.  carbon  that  are  in  a  metric  ton  of  iron  require      — — -• 

45 

=  145  kg.  ore.     This  amount  of  ore  heated  to  800°  C.  holds 

145  X  0.2  X  800  =  23200    cals.,    which    equals    -      —  =  26.8 

864.5 

kw.  hrs.,  an  amount  that  helps  the  electric  furnace  considerably, 
so  that  the  use  of  preheated  ore  is  worth  consideration,  if  the 
cost  of  preheating  is  not  too  high. 

There  are  also  proposals  to  carry  out  air-blast  refining,  similar 
to  the  Bessemer,  in  the  electric  furnace.  With  arc  furnaces  the 
electrodes  would  have  to  be  drawn  up  high  during  the  blowing, 
so  that  during  this  operation  no  heat  would  be  supplied,  and  the 
bath  would  chill,  if  there  were  not  sufficient  silicon  and  phos- 
phorus present  to  balance  the  heat  lost,  and  bring  the  metal  to 
the  casting  temperature  of  soft  steel.  In  this  case  the  bath 
must  be  alternately  electrically  heated,  then  blown  for  a  short 
time,  but  this  gives  so  many  operating  troubles  that  the  intended 
saving  due  to  time  saved  with  blowing  is  not  realized. 

Iron  low  i»  silicon  and  phosphorus,  that  cannot  be  handled 
by  either  the  acid  or  basic  Bessemer,  may  be  refined  with  a  blast 
of  air  in  the  induction  furnace,  for  here  the  bath  can  be  heated 
during  the  blow.  The  following  rough  calculations  give  some 
information  on  the  probable  results  with  a  lo-ton  furnace  and 
a  pig  iron  with  3%  carbon,  and  a  temperature  of  1300°  C. 

10  tons  iron  contain  300  kg.  carbon,  which  would  require 

(12  C  +  160  =  28  CO)  —  — - —  =  400  kg.  O,  100  kg.  air  con- 
tain 23  kg.  O,  so  that  400  kg.  O  correspond  to 

1740  kg.  air.  The  temperature  of  the  bath  must  be  raised  from 
1300°  to  1650°  C.,  that  is  35o°C. 

The  blast  may  leave  the  bath  at  an  average  temperature  of 


THE   ELECTRO-METALLURGY   OF  IRON  AND  STEEL  '425* 

1500°  C.,  although  this  value  is  probably  too  small,  for  the 
carbon  in  the  bath  heated  to  1300°  C.  will  burn  at  a  high  tem- 
perature, and  it  appears  doubtful  whether  the  very  hot  gas 
produced  will  give  its  heat  to  the  bath  completely  enough  to 
escape  at  only  1500°  C. 

There  is  therefore  the  following  amount  of  electric  energy 
conducted  to  the  bath. 

10000  kg.  iron  heated  350°  C.    10000  X  0.2  X  350  =  700,000 
1740  kg.  air  heat  to  1500°  C.     1740  X  0.3  X  1500  =  783,000 

1,483,000 
Brought  in: 

300  kg.   C  burnt  to  CO   741,900 

Leaving 741,000 

This  corresponds  to  -g^°°°  =857  kw.  hrs. 

Therefore  an  electric  induction  furnace  of  10  tons  capacity 
will  operate  with  about  800  to  900  kw.  hrs.  If  the  efficiency  of 
the  furnace  is  taken  as  60%,  then  480  to  540  kw.  will  be  sufficient 
to  heat  the  bath.  This  shows  that  the  carbon  can  be  thoroughly 

removed,  in  -f£  to  — ,  that  is  iK~i^  hours.    The  time  interval 

400      540 

under  these  conditions  compared  with  that  of  the  other  air-blast 
refining  processes  is  very  considerable.  Air-blast  refining  must 
therefore  be  carried  out  extremely  slowly,  or,  with  frequent 
interruptions.  The  proposals  to  refine  in  this  way  have  so  far 
found  no  practical  application. 

From  all  this  it  follows  that,  if  there  is  a  mixer  available 
it  is  a  good  thing  in  all  cases  to  bring  about  as  complete  refining 
as  possible  in  the  mixer,  and  so  relieve  the  electric  furnace. 
Better  economic  results  are  obtained  in  refining  pig  iron  if  large 
amounts  of  mild  steel  scrap  are  available  to  melt  with  it,  so  that 
only  a  hard  steel-like  product  remains  to  be  treated. 

The  problem  of  pig-iron  refining  in  the  electric  furnace  now 
approaches  solution,  because,  for  example,  for  railroad  material 
there  is  an  inclination  to  use  harder  qualities  of  steel  than  are 


426   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

used  now.  If,  in  a  case  like  this,  the  pig  iron  to  be  used  is 
sufficiently  low  in  phosphorus  so  that  no  refining  is  necessary, 
to  give  a  steel  low  enough  to  meet  specifications,  then  carbon 
alone  has  to  be  removed.  In  such  a  case  the  electric  furnace 
could  work  economically  in  many  places.  Also  with  specifica- 
tions calling  for  very  low  phosphorus  in  the  steel  the  bath  high 
in  carbon  and  phosphorus  can  be  dephosphorized  without  re- 
moving the  carbon,  as  mentioned  above,  by  keeping  the  tem- 
perature low  and  forming  an  easily  fusible  basic  slag,  containing 
oxide  of  iron,  which  is  drawn  off  when  the  phosphorus  is  low 
enough  in  the  steel. 

The  refining  of  pig  iron  in  the  electric  furnace  is  not  advan- 
tageous if  a  low  carbon,  absolutely  phosphorus  free,  material 
has  to  be  made  from  a  high  phosphorus  pig  iron.  In  order  to 
remove  the  phosphorus  the  carbon  must  first  be  completely 
taken  away,  and  the  bath  even  overrefined  to  a  certain  extent. 
In  general  for  this  purpose  the  electric  furnace  cannot  compete 
economically  with  the  open  hearth.  Further,  in  this  case  the 
cost  of  fuel  and  of  current  have  to  be  weighed  against  each 
other. 

If  the  pig  iron  to  be  refined  is  high  in  silicon,  as  well  as 
phosphorus,  two  electric  furnaces  can  be  used,  one  with  an  acid 
lining  for  removing  silicon  and  carbon,  the  other  with  a  basic 
lining  to  remove  the  phosphorus.  Still  such  an  iron  can  be  worked 
in  the  basic  furnace  in  which  case  a  sufficient  amount  of  lime 
must  be  added  to  prevent  the  lining  from  being  attacked.  Fi- 
nally, the  deoxidation,  etc.,  can  be  carried  out  in  a  third  furnace 
with  an  acid  lining,  or  in  crucibles,  and  many  combinations  of 
the  crucible,  open  hearth  furnace,  mixer,  converter,  etc.,  are 
possible,  the  suitability  of  which  must  be  decided  for  each 
separate  case. 

The  output  when  refining  with  ore  is  extraordinarily  high, 
because  there  is  no  loss  and  because  of  reduction  from  the  ore,  so 
that  it  is  over  100%. 


THE   ELECTRO-METALLURGY   OF   IRON  AND  STEEL  127 

THE  PRODUCTION  OF  SPECIAL  QUALITY  STEEL  IN  THE 
ELECTRIC  FURNACE 

High  quality  steel  production  aims  at  the  melting  of  the 
softest  to  the  hardest  qualities  as  desired  in  both  alloy  and  plain 
steels.  Steels  that  will  meet  the  most  rigid  requirements  in 
regard  to  low  sulphur  and  phosphorus  on  the  one  hand,  and  on 
the  other  hand  be  as  free  from  oxygen  as  possible  and  in  this 
respect  be  equal  to  crucible  steel. 

The  best  material  up  to  the  present  has  been  made  by  the 
crucible  process,  special  care  being  paid  to  the  kind  of  raw 
material  charged.  The  use  of  the  purest  materials  is  a  first 
requirement  for  the  crucible  process,  for  naturally  no  removal 
of  sulphur  and  phosphorus  is  possible  to  any  considerable  extent. 
Indeed  this  dependence  on  certain  kinds  of  iron,  which  meet 
the  guarantee  of  absolute  purity,  altogether  apart  from  the 
cost,  has  finally  been  the  reason  for  the  introduction  of  the 
electric  furnace,  as  it  made  the  material  forming  the  charge 
independent  of  a  fixed  source  of  supply.  The  general  strike  in 
Sweden  during  1911  has  opened  the  eyes  of  the  leaders  in  this 
industry  to  the  disadvantages  that  may  come  when  one  is 
forced  to  use  a  certain  material  alone. 

In  comparison  with  this  the  electric  furnace  offers  the  great 
advantage  that  it  is  not  dependent  on  any  certain  special  raw 
material,  for  the  most  impure  materials  can  be  refined  so  that 
they  become  even  better  than  the  purest  Swedish  charcoal  iron 
in  regard  to  purity  from  phosphorus  and  sulphur.  At  the  same 
time  deoxidation  takes  place  just  as  completely  as  in  the  crucible 
because  a  purely  reducing  atmosphere  is  maintained,  the  steel 
can  be  held  as  long  as  desired,  and  the  temperature  can  be  regula- 
ted with  more  certainty  than  in  furnaces  heated  with  fuel.  Sim- 
ilar conditions  are  not  offered  by  any  other  metallurgical  furnace, 
for  in  them  the  action  of  the  flame  on  the  bath  cannot  be  entirely 
prevented. 

From  all  this  it  is  seen  that  electric  steel  is  at  least  of  equal 
value  to  crucible  steel,  for  it  can  be  produced  practically  free 
from  phosphorus,  sulphur,  and  non-metallic  inclusions.  There- 


428  ELECTRIC  FURNACES  IN  THE   IRON  AND  STEEL  INDUSTRY 

fore  the  use  of  the  electric  furnace  gives  the  advantage,  that  in 
it  ordinary  low  carbon  steel  can  be  improved  and  made  equal 
to  the  very  best  qualities  of  crucible  steel,  for  from  the  low  carbon 
steel: 

(1)  Phosphorus  and  sulphur  are  completely  removed. 

(2)  It  is  totally  deoxidized. 

(3)  It  is  freed  from  slags  and  inclusions. 

(4)  It  is  accomplished  at  a  lesser  cost  per  ton. 

PRODUCTION  OF  SPECIAL  QUALITY  STEEL  IN  THE  ELECTRIC  FUR- 
NACE  FROM   PREVIOUSLY   REFINED    METAL   WITH   LOW 
PHOSPHORUS  AND  SULPHUR 

It  is  a  side  issue  in  what  way  the  steel  is  prerefmed,  whether 
in  the  converter,  in  the  basic  or  acid  open  hearth,  or  in  any 
other  way.  Also  the  material  can  either  be  charged  liquid  or 
cold,  but  in  the  latter  case,  the  electric  furnace  will  also  be  used 
for  melting.  If  the  electric  furnace  is  worked  in  combination 
with  an  ordinary  steel  plant  from  which  it  obtains  its  charge, 
then  it  is  most  suitable  to  pour  a  part  of  the  steel  works  charge  in- 
to the  electric  furnace  before  the  deoxidizing  additions  are  made. 
On  the  other  hand,  if  larger  heats  are  made  in  the  steel  works 
than  the  electric  furnace  is  able  to  take,  or  for  other  reasons,  then 
the  bath  of  steel  to  which  the  additions  have  already  been  made 
can  be  partially  poured  into  the  electric  furnace.  Naturally 
it  is  preferable  that  the  electric  furnace  be  able  to  take  the  whole 
heat  with  the  restriction  that  the  building  of  very  large  electric 
furnaces  is  at  present  troublesome.  In  regard  to  this  the  first 
part  of  the  book  should  be  consulted. 

In  the  case  we  are  considering,  the  aim  of  the  electric  furnace 
'    is  to  improve  the  steel  and  to  produce  a  material  of  equal  value 
to  open  hearth,  or  crucible  steel,  in  particular: — 

(1)  To  recarburize  the  bath  to  the  required  hardness. 

(2)  To  deoxidize  the  bath. 

(3)  To  bring  about  the  removal  of  ga£  and  slag  inclusions. 

(4)  To  alloy  the  bath  as  desired. 

Such  a  process  can  be  profitable,  for  example,  if  there  is  a 
Bessemer  plant  operating,  and  it  is  desired  to  produce  from  the 


THE   ELECTRO-METALLURGY   OF   IRON  AND   STEEL  429 

Bessemer  steel  material  equal  to  high  grade  open  hearth,  which 
will  be  required  for  various  purposes  such  as  boiler  plate,  etc. 
Such  material  finished  by  the  electric  furnace  is  extremely 
suitable  for  particular  purposes,  so  much  the  more  that  it  rolls 
and  forges  well  and  shows  considerably  increased  physical 
properties.  There  is  also  less  second-grade  material. 

If  material  is  charged  into  the  electric  furnace  to  which  no 
deoxidizing  additions  have  been  made,  then  it  has  to  be  first 
completely  deoxidized,  and  the  production  of  steel  of  a  satis- 
factory quality  requires,  in  the  first  place,  that  this  deoxidation 
be  carried  out  very  carefully.  As  shown  in  a  previous  chapter 
it  can  be  done  in  many  ways,  with  ferro-manganese,  ferro-silicon, 
etc.  Which  of  these  materials  should  be  used  depends  on  the 
quality  of  steel  that  has  to  be  produced,  particularly  whether 
it  is  to  be  a  low  or  high  manganese. 

If  a  product  is  to  be  made  as  low  in  manganese  as  possible 
then  it  is  best  to  carry  out  the  deoxidation  with  ferro-silicon. 
Immediately  after  pouring  the  charge  into  the  electric  furnace 
the  first  addition  of  ferro-silicon  should  be  made,  preferably  in 
pieces  about  the  size  of  one's  fist,  and  at  the  same  time  the 
bath  should  be  covered  with  an  easily  fusible  slag  to  exclude 
the  air. 

The  kind  of  slag  is  governed  by  the  furnace  lining:  with  a 
basic  hearth  a  neutral  or  basic  slag  is  charged;  with  a  neutral  or 
acid  hearth,  on  the  other  hand,  one  of  greater  acidity.  A  suit- 
able mixture  of  lime  and  sand  with  more  or  less  fluor-spar  may  be 
used  to  form  the  slag,  all  of  proper  size.  In  regard  to  the  amount 
of  slag  it  should  be  mentioned  that  the  bath  has  only  to  be 
completely  covered.  Furnaces  of  greater  capacity  that  work 
with  a  deep  bath  use,  therefore,  a  lower  percentage  of  slag  than 
those  of  less  capacity  which  expose  more  surface  per  ton. 

The  first  addition  of  ferro-silicon  is  given,  before  the  bath 
is  covered  with  slag  in  order  to  save  time  in  the  first  place, 
and  secondly  to  prevent  the  light  ferro-silicon  from  being  en- 
closed in  the  slag,  which  is  quite  thick  at  first.  The  slag  first 
turns  black  due  to  the  absorption  of  oxide  of  iron  from  the  bath, 
for  a  condition  of  equilibrium  is  formed  between  the  oxide  dis- 


430  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

solved  in  the  bath  and  the  slag.  For  complete  deoxidation  it  is 
therefore  absolutely  necessary  that  the  slag  contain  no  oxide, 
and  so  it  must  always  be  snow  white.  This  is  produced  by 
sprinkling  a  suitable  reducing  agent  on  the  slag  when  it  shows  a 
dark  color,  and  maintaining  a  neutral  or  reducing  atmosphere. 
In  the  induction  furnace  fine  ferro-silicon,  about  pea  size,  is 
used  in  this  way,  being  added  from  time  to  time  in  small  amounts. 
In  the  arc  furnace  this  ferro-silicon  can  be  produced  from  the 
slag  if  carbon  is  added.  Which  of  the  two  methods  is  the  cheaper 
we  will  not  investigate. 

If  the  slag  keeps  snow  white  then  the  melter  takes  pouring 
tests  and  convinces  himself  of  the  condition  of  the  steel,  and  if  it 
does  not  yet  pour  quietly,  adds  more  pieces  of  ferro-silicon  to 
the  bath  until  a  further  test  gives  a  good  result.  A  completely 
deoxidized  steel,  melted  with  a  white  slag,  must  pour  without 
trouble.  Alloys  such  as  nickel,  manganese,  chromium,  etc., 
can  now  be  added  in  the  theoretical  amounts,  for  no  slagging 
of  these  additions  can  take  place  under  the  white  slag  covering. 
No  preheating  is  necessary,  and  also  the  cheaper  ferro  alloys, 
high  in  carbon,  can  be  used  in  the  induction  furnace  for,  due 
to  the  movement  of  the  metal  bath  in  this  furnace,  it  is  impossible 
for  carbides  to  remain  undissolved. 

In  making  a  steel  with  low  to  average  manganese  content  it  is 
the  best  to  give  first  an  addition  of  ferro-silicon,  after  which  the 
bath  is  covered  with  slag.  The  final  deoxidation  can  now  be 
made  with  ferro-manganese,  spiegel,  etc.  After  this  the  slag  will 
first  darken,  due  to  the  manganese  reacting  with  the  oxide  of 
iron  forming  MnO,  which  enters  the  slag.  As  mentioned  above 
the  first  requirement  for  complete  deoxidation  is  that  the  slag 
be  snow  white.  The  black  slag  produced  must,  therefore,  be 
reduced  in  a  suitable  manner  and  made  white. 

In  the  induction  furnace  ferro-silicon  again  serves  as  a 
suitable  reducing  agent  and  carbon  in  the  arc  furnace,  both  of 
which  are  sprinkled  on  the  slag.  The  reduced  manganese  goes 
again  into  the  slag.  It  therefore  passes  through  a  cycle  and 
really  only  serves  as  a  bearer  of  the  oxygen  contained  in  the 
metal,  so  that  the  deoxidation  can  be  carried  out  with  very  small 


THE  ELECTRO-METALLURGY   OF   IRON  AND   STEEL  431 

amounts  of  manganese,  and  a  final  material  with  a  moderate 
percentage  of  manganese  can  be  produced. 

Instead  of  ferro-manganese,  manganese  ore  can  be  used, 
and  in  the  induction  furnace  this  ore  is  selectively  reduced  by 
ferro-silicon  rather  than  with  carbon,  but  in  the  arc  furnace  on 
the  other  hand  the  one  would  be  reduced  by  carbon  under  the 
influence  of  the  arc.  It  is  not  necessary  to  consider  here  whether 
it  is  the  cheaper  to  use  ferro-manganese  melted  in  the  blast 
furnace  or  to  reduce  manganese  in  the  electric  furnace  from 
manganese  ore.  The  remainder  of  the  process  of  melting  is 
the  same  as  that  described  under  the  production  of  steel  free  from 
manganese. 

If  the  material  has  to  be  harder,  that  is  higher  in  carbon 
than  the  material  charged,  then  after  the  first  addition  of  ferro- 
silicon  before  the  slag  is  made,  the  necessary  amount  of  carbon 
is  added  to  the  bath.  A  small  excess  is  given,  depending  on  the 
size  and  the  physical  condition  of  the  carbonizing  material  used, 
for  a  part  is  burned  as  it  is  charged  into  the  furnace.  Then 
comes  the  slag  formation,  and  it  is  well  to  take  a  test  and  make 
a  quick  color  carbon  determination  to  see  whether  the  metal  is 
of  the  right  hardness.  The  further  process  is  the  same  as  that 
used  for  the  production  of  low  manganese  steel.  The  tempera- 
ture is  held  at  such  a  degree  that  the  small  impurities  caused  by 
the  reduction  can  separate  readily  and  is  gradually  increased 
to  the  proper  casting  temperature.  It  must  be  remembered 
that  the  slag  formation  requires  a  certain  amount  of  heat  as 
also  the  solution  of  carbon,  if  any  is  added,  and  so  cools  the 
bath. 

At  the  beginning  of  the  debxidation  it  is  well  to  give  an 
addition  of  ferro-silicon  even  when  melting  high  carbon  material. 
If  carbon  is  added  to  the  bath  before  the  ferro-silicon  then  there 
is  a  vigorous  action,  and  a  considerable  loss  of  carbon  cannot 
be  avoided.  At  the  most,  therefore,  one  can  only  add  a  part 
of  the  carbon  before  the  ferro-silicon,  and  after  the  deoxidaticn 
the  rest  must  be  added  in  a  special  operation  to  give  the  hardness 
required.  Also  by  the  addition  of  carbon  before  the  ferro- 
silicon  scarcely  any  ferro-silicon  will  be  saved,  and  on  the  other 


432  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

hand  it  only  increases  the  time  of  the  operation  and  the  work 
in  the  furnace. 

If  the  ordinary  forging  and  pouring  tests  are  favorable  then 
the  casting  of  the  heat  is  proceeded  with.  The  slag  also  is 
poured  into  the  casting  ladle  in  order  to  protect  the  metal  from 
the  influence  of  the  air  in  the  first  place,  and  secondly  to  prevent 
the  slag  sticking  to  the  hearth  of  the  empty  furnace,  and  attack- 
ing the  lining.  Due  to  the  total  deoxidation  the  electric  steel 
casts  so  quietly  that  the  addition  of  aluminum  to  the  stream 
during  pouring  is  absolutely  unnecessary,  so  that  in  this  respect 
the  quality  of  the  metal  does  not  suffer.  Casting  is  carried  out 
in  just  the  same  way  as  in  plants  making  high  quality  steels. 

As  a  conclusion  it  may  be  mentioned  that  during  this  finishing 
process  considerable  desulphurization  is  brought  about  by  the 
silicon  present,  even  when  it  is  not  intended,  so  that  in  this 
respect  the  after  treatment  of  low  carbon  steel  in  the  electric 
furnace  means  a  raiher  considerable  improvement  in  quality. 

If  an  addition  of  ferro-manganese  for  deoxidation  has  already 
been  made  in  the  converter,  open  hearth,  etc.,  then  after  pouring 
into  the  electric  furnace  an  easily  fusible  basic  slag  alone  has 
to  be  made  and  kept  constantly  white,  that  is  free  from  oxide. 
This  is  brought  about  as  mentioned  above  by  ferro-silicon  in 
the  induction  furnace  or  just  as  well  by  carbon  in  the  arc  furnace, 
where  silicon  is  reduced  from  the  slag  by  the  influence  of  the 
arc.  This  assumes  that  the  steel  poured  into  the  electric  furnace 
already  contains  the  necessary  percentage  of  silicon,  but  if  this 
is  not  the  case  then  before  the  formation  of  the  slag  the  corre- 
sponding addition  of  ferro-silicon  is  given.  Naturally  in  this 
process  also  there  is  a  lowering  of  the  sulphur  of  the  charge, 
even  if  such  is  not  intended. 


PRODUCTION   OF    SPECIAL   QUALITY    STEEL   IN   THE    ELECTRIC 
FURNACE  FROM  PREVIOUSLY   REFINED  METAL  WITH  CON- 
SIDERABLE PHOSPHORUS  AND   SULPHUR 

Here  also  it  does  not  matter  in  what  way  the  steel  is  pre- 
refined,  or  whether  it  is  charged  hot  or  cold  so  that  the  electric 
furnace  has  to  be  also  Used  as  a  melting  furnace.  The  aim  of 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  433 

the  after  treatment  in  the  electric  furnace  is  to  raise  the  quality 
either  to  that  of  open  hearth  or  the  best  crucible  steel.  The 
metallurgical  process  in  the  electric  furnace  must  therefore  im- 
prove the  steel  in  regard  to  the  following  points: 

(1)  Eliminate  the  phosphorus. 

(2)  Deoxidize  and  desulphurize. 

(3)  Remove  the  gas  and  slag  inclusions. 

(4)  Recarburize  or  alloy  according  to  requirements. 

In  regard  to  the  removal  of  phosphorus  and  sulphur  both 
elements  cannot  be  removed  from  the  bath  in  one  operation,  for 
the  removal  of  the  phosphorus  takes  place  by  an  oxidizing  or 
refining  process,  and  that  of  the  sulphur,  on  the  other  hand,  by 
a  reducing  process: 

FeS  +  CaO  +  C  =  Fe  +  CaS  +  C  O. 

These  operations  must,  therefore,  be  carried  out  one  after 
the  other,  and  it  is  similar  in  principle  whether  the  bath  is  de- 
sulphurized first  and  then  dephosphorized,  or,  on  the  other  hand, 
dephosphorized  first  and  then  desulphurized.  Which  of  the 
two  ways  is  the  most  suitable  depends  on  the  composition  of 
the  charge  that  is  put  into  the  electric  furnace  and  on  the  kind 
of  steel  to  be  produced. 

If  the  metal  as  charged  has  had  no  additions  so  that  it  is 
not  yet  deoxidized,  then  it  is  best  to  dephosphorize  first  of  all 
as  the  necessary  conditions  are  present.  The  total  removal  of 
the  phosphorus  requires  an  overoxidation  of  the  bath,  so  that 
the  metal  gives  a  seamy,  that  is  a  red  short,  forging  test.  When 
using  a  charge  that  is  still  oxidized  therefore  only  a  basic  slag 
has  to  be  charged  to  favor  the  soaking  of  the  bath  with  oxygen, 
and  at  the  same  time  give  conditions  so  that  the  phosphoric 
acid  formed  is  immediately  combined  with  lime.  The  require- 
ments in  regard  to  freedom  from  sulphur  on  the  part  of  the  slag- 
making  materials  are  not  particularly  high,  for  the  bath  has  to  be 
desulphurized  afterwards  anyhow,  but  it  is  well  to  use  materials 
as  low  in  sulphur  as  possible,  so  as  not  to  raise  the  sulphur  in  the 
bath.  Also  the  phosphoius  percentage  of  the  ore  is  without 
influence,  for  an  oxidized  bath  cannot  reduce  phosphorus,  and 


434  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

is  therefore  unable  to  take  phosphorus  from  the  ore  or  lime- 
stone. 

If  it  is  desired,  on  the  other  hand,  to  desulphurize  first  then 
the  bath  must  be  first  completely  deoxidized,  and  after  the  re- 
moval of  sulphur  the  bath  must  be  oxidized  again  to  remove  the 
phosphorus.  The  whole  manipulation  of  the  deoxidizing,  there- 
fore, gives  no  lasting  result,  and  at  the  same  time  only  the  purest 
ore  and  limestone  can  be  used  to  form  the  refining  slag  so  as  to 
prevent  absorption  of  sulphur  by  the  bath. 

On  the  other  hand  if  the  charge  has  already  had  an  addition 
of  f erro-manganese  in  the  converter,  open  hearth,  etc. ;  and  if  a 
very  soft  steel  has  to  be  made  with  the  lowest  possible  phos- 
phorus and  sulphur  and  also  practically  free  from  silicon,  then 
it  is  best  to  desulphurize  first.  In  this  way  one  can  work  with 
a  small  amount  of  silicon,  and  the  low  silicon  remaining  in  the 
bath  is  removed  during  dephosphorizing.  The  heat  is  then 
finished  with  the  addition  of  ferro-manganese,  and  is  cast  just 
as  in  the  open  hearth  process,  keeping  the  slag  back.  Here  also 
it  is  necessary  to  use  ore  and  lime  free  from  sulphur  to  prevent 
the  bath  again  taking  up  sulphur  during  the  subsequent  opera- 
tions. The  quality  produced  is,  however,  only  equal  to  that  of 
good  open  hearth  not  crucible  steel.  If  sulphur-free  burnt 
lime  is  not  available  then  it  is  well  to  use  raw  limestone  if  the 
sulphur  is  low  enough.  Apart  from  this  and  some  other  special 
cases  the  charge,  prerefined  and  then  poured  into  the  electric 
furnace,  will  always  be  dephosphorized  first  whether  deoxidizing 
additions  have  been  already  given  in  the  preliminary  furnace 
or  not.  This  is  done  because:  (i)  With  desulphurizing  first 
the  silicon  used  is  again  removed  during  the  dephosphorizing. 
Therefore  the  amount  of  ferro-silicon  used  is  unnecessarily  in- 
creased; (2)  the  total  deoxidation,  which  is  necessary  for  de- 
sulphurization,  would  be  made  of  no  use  by  the  subsequent 
oxidation,  (3)  the  ore  and  limestone  used  for  the  refining  slag 
have  to  be  very  free  from  sulphur. 

Immediately  after  pouring  the  charge  into  the  electric 
furnace  a  refining  slag  should  be  formed  with  ore  and  lime. 
The  size  of  these  materials  should  not  be  too  great  as  otherwise 


THE  ELECTRO-METALLURGY  OF  IRON  AND   STEEL  435 

they  only  fuse  together  with  difficulty,  that  is,  the  formation 
of  the  slag  takes  too  long  and  the  time  of  the  heat  is  increased. 
On  the  other  hand  there  is  no  limit  to  the  fineness  of  the  material, 
so  that,  for  example,  unbriquetted  concentrates  can  be  used. 
The  burnt  lime  is  best  broken  up  just  before  charging,  for  it 
quickly  takes  up  moisture  and  carbon-dioxide  from  the  air. 

The  amount  of  slag  necessary  is  proportionally  small,  espe- 
cially if  dephosphorization  has  already  taken  place  to  some 
extent,  for  instance,  to  0.1%.  The  bath  need  not  be  well  covered 
by  the  slag,  although  dephosphorization  naturally  takes  place 
more  quickly  if  the  slag  covering  is  not  too  small.  On  the  other 
hand  it  is  well  not  to  unnecessarily  increase  the  amount  of  slag 
so  as  to  avoid  loss  of  heat.  In  the  induction  furnace,  work  hi 
a  high  manganese  charge,  that  is  one  already  deoxidized  in  the 
first  furnace,  it  is  well  to  make  a  slag  with  i%  ore  and  2%  lime 
of  the  weight  of  the  charge.  If  the  forging  test  shows  that  the 
bath  has  the  right  percentage  of  phosphorus,  then  the  slag  is 
drawn  oil",  and  the  last  traces  removed  by  means  of  fresh  lime 
thrown  over  the  bath.  This  thickens  the  remainder  of  the  slag 
so  that  it  can  be  easily  removed. 

If  a  high  phosphorus  charge  is  to  be  worked,  then  it  is  well 
not  to  charge  the  whole  amount  of  slag  necessary  at  one  time  for, 
as  mentioned  before,  it  is  not  recommended  to  work  with  too 
large  a  slag  volume  in  the  electric  furnace.  In  this  case  it  is 
better  to  charge  the  ordinary  small  amount  of  slag,  remove  it 
when  completely  used  up,  and  then  form  a  new  slag  of  the  same 
weight.  This  should  be  repeated  as  required.  Such  a  case 
can  happen  in  practise  if  the  electric  furnace  charge  is  taken 
from  a  heated  prerefming  furnace,  such  as  a  Wellman-Talbot 
furnace,  in  which  by  exceeding  the  capacity  a  material  is  produced 
that  is  high  in  phosphorus. 

If  the  electric  furnace  is  to  be  used  continuously  for  the 
refining  of  such  high  phosphorus  charges,  then  it  is  well  to  figure 
on  this  in  the  construction  of  the  furnace.  A  shallow  bath  but 
a  large  surface  should  be  used  in  order  to  give  the  refining  slag  a 
large  attacking  surface,  and  to  shorten  the  time  of  the  process. 
On  the  other  hand  the  surface  of  the  bath  should  not  be  too  great 


436  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

for,  in  this  way,  the  radiation  loss  increases  and  the  efficiency 
of  the  furnace  drops.  These  are  important  points  for  the  de- 
signers of  the  furnace,  namely,  to  make  the  hearth  the  right  size 
and  shape  to  properly  meet  the  conditions,  and  in  this  respect 
experience  obtained  with  open  hearth  furnaces  will  be  valuable. 
If  a  high  phosphorus  charge  is  worked,  with  several  refining 
slags,  then  the  first  slag  is  very  low  in  iron  but  high  in  lime  and 
phosphoric  acid.  These  slags  are  of  some  value  in  agriculture 
as  low  phosphate  slags,  so  that  they  need  not  be  thrown  away. 
The  succeeding  slags,  however,  are  rich  in  oxide  of  iron  and  low 
in  phosphorus,  and  can  be  used  as  a  first  slag  for  subsequent 
heats  and  so  be  used  more  completely.  If  the  fluxes  are  used 
to  exhaustion  then  the  consumption  of  ore  and  lime,  in  reference 
to  the  finished  material,  is  considerably  reduced. 

The  bath  can  now  be  deoxidized,  carburized,  and  desul- 
phurized. The  removal  of  the  oxygen  and  sulphur  takes  place 
together,  the  first  by  means  of  ferro-silicon,  carbon,  or  ferro- 
manganese  depending  on  the  kind  of  material  to  be  melted;  the 
latter  by  the  addition  of  ferro-silicon  and  in  the  arc  furnace  by 
silicon  or  calcium  reduced  from  the  slag  by  carbon  under  the 
influence  of  the  arc. 

First  an  addition  of  ferro-silicon  is  made  that  can  be  a  little 
more  in  amount  than  is  necessary  for  deoxidation  alone  because 
of  the  desulphurization  also  taking  place.  In  general  the  opera- 
tion is  exactly  the  same  as  described  in  the  previous  section, 
namely:  "The  production  of  electric  furnace  material  from 
previously  refined  metal  with  low  phosphorus  and  sulphur." 

It  may  be  mentioned  that  tungsten  has  similar  desulphuriz- 
ing properties  to  silicon,  so  that  tungsten  heats  can  also  be  made 
extremely  low  in  sulphur. 

A  peculiar  phenomenon  must  be  mentioned  which  can 
happen  under  certain  conditions  with  non-expert  handling  of 
the  electric  furnace.  As  already  said  a  well  deoxidized  charge 
pours  quietly,  and  only  pipes  a  little  on  solidifying,  depending 
on  the  temperature  and  the  silicon.  On  the  other  hand,  if  the 
heat  is  made  too  hot,  if  the  bath  is  not  completely  covered  with 
slag,  if  air  can  enter  the  furnace,  or  if  the  deoxidation  slag  is 


THE  ELECTRO-METALLURGY   OF  IRON  AND  STEEL  437 

not  kept  sufficiently  free  from  metal,  then  the  steel  casts  very 
badly,  even  though  it  may  contain  several  tenths  per  cent,  of 
silicon,  the  forging  tests  will  show  the  properties  of  an  oxidized 
material.  The  causes  for  this  phenomenon  are  not  at  present 
very  clear,  but  it  appears  probable  that  at  high  temperatures  a 
part  of  the  silicon  occurs  dissolved  in  the  metal  as  a  suboxide, 
probably  with  the  formula  SiO.  Because  of  the  similarity 
between  silicon  and  carbon  the  possibility  of  an  alloy  of  iron  and 
silicon-suboxide  can  be  thought  of,  for,  as  mentioned  before,  the 
existence  of  an  alloy  of  iron  with  carbon-monoxide  is  probable. 

THE  METALLURGICAL  COURSE  OF  AN  ELECTRIC  FURNACE 
CHARGE 

The  course  of  the  metallurgical  reactions  in  the  Heroult 
and  the  Rb'chling-Rodenhauser  furnace  is  given  in  the  two 
accompanying  diagrams  (page  409).  The  curves  for  the  Her- 
oult furnace  were  pubb'shed  by  Thallner  in  No.  5,  1909,  of 
Kohle  und  Erz,  and  are  taken  from  a  heat  in  a  3-ton  furnace; 
while  the  diagram  of  the  Rochling-Rodenhauser  furnace  is  taken 
from  an  ordinary  heat  made  at  Volklingen  in  an  8-ton  single- 
phase  furnace  built  up  to  take  5  to  6  tons. 

From  a  comparison  of  the  two  diagrams  it  is  seen  first  that 
the  time  of  heat  in  the  Heroult  was  twenty  minutes  longer  than 
in  the  Rochling-Rodenhauser  furnace,  notwithstanding  that  the 
former  was  only  worked  with  a  3-ton  heat,  while  the  latter  had  5 
tons. 

Also,  the  material  made  in  the  Rochling-Rodenhauser  is  at 
least  just  as  pure  as  that  produced  in  the  Heroult,  notwithstand- 
ing that  a  much  more  impure  charge  was  worked  in  the  former. 
The  oxidation  period  is  distinguished,  in  the  Rochling-Roden- 
hauser furnace,  especially  at  the  beginning,  by  an  extraordinarily 
quick  removal  of  the  phosphorus  and  manganese  from  the 
steel.  For  instance,  in  the  first  twenty  minutes  the  phosphorus 
drops  from  0.06  to  0.025,  that  is  0.035%,  while  in  the  Heroult 
furnace  it  is  only  lowered  from  0.03  to  0.02,  that  is  0.01%,  in  the 
same  time. 

Also  the  manganese  drops  from  0.49  to  0.12,  that  is  0.37%  in 


438   ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

the  first  hour  in  the  Rochling-Rodenhauser  furnace,  while  in  the 
Heroult  furnace  in  the  same  time  it  is  only  lowered  from  0.21  to 
is  0.1%. 

From  this  it  follows  that  the  Rochling-Rodenhauser  furnace 
must  be  considered  as  a  good  oxidizing  furnace.  The  lowering 
of  the  phosphorus  content  of  the  slag,  which  is  to  be  noticed 
during  the  oxidation  period  with  both  furnaces,  is  due  to  the 
slag  being  diluted  from  time  to  time  by  the  addition  of  roll  scale. 

The  removal  of  sulphur  during  the  oxidation  period  is  rela- 
tively unimportant  with  both  furnaces,  and  only  after  the 
recarburization,  or  after  the  formation  of  the  final  slag,  does  the 
real  desulphurization  begin.  During  this  period  the  sulphur 
is  lowered  in  the  Heroult  furnace  from  0.07  to  0.012%,  while 
in  the  Rochling-Rodenhauser  a  desulphurization  from  0.065 
to  traces  is  brought  about.  That  the  ability  of  the  slag  in  the 
Rochling-Rodenhauser  furnace  to  absorb  sulphur  is  at  least 
as  great  as  that  in  the  Heroult  furnace  is  seen  from  the  sulphur 
content  of  the  slag,  which  is  1.25%  in  the  first  case,  and  only 
about  0.06%  in  the  latter  as  shown  by  the  curves.  The  amounts 
of  slag-making  constituents  used  in  both  cases  are  shown  in  the 
diagrams,  so  that  all  the  details  of  the  refining  operation  are 
given  that  are  of  interest. 

THE  SPECIAL  QUALITIES  OF  ELECTRIC  IRON  AND  STEEL 

As  already  shown  any  material  from  the  mildest  to  the 
hardest  quality  can  be  made  in  the  electric  furnace.  Electric 
furnace  material  is  distinguished  by  its  freedom  from  gas  and 
slag  inclusions,  and  can  easily  be  produced  with  very  low  man- 
ganese and  completely  free  from  phosphorus  and  sulphur,  and 
as  soft  and  forgeable  as  the  Swedish  qualities.  This  low  carbon 
electric  steel  can  easily  be  alloyed,  for  instance  with  silicon,  for 
making  material  for  dynamo  plates,  etc.,  the  production  of 
which  in  the  open  hearth  furnace  is  troublesome  because  of  the 
necessary  low  casting  temperature.  The  use  of  the  electric 
furnace  for  this  purpose  means,  therefore,  considerably  easier 
operation.  Also  the  softest  material  can  be  flattened  out  very 
thin  without  showing  red  shortness,  and  can  be  used  for  punching 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STIiKL 


439 


lU-ducinff  period 


Refining  curves  for  the  Rochling-Rodenhauser  Refining  curves  for  the  Heroult  furnace, 

furnace. 


440  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

and  deep  drawn  work,  deep  stamping,  etc.,  for  everything  where 
value  is  put  on  good  malleability;  also  for  the  production  of 
chains,  the  making  of  tools,  etc.,  and  further  in  those  cases 
where  especially  soft  open  hearth  qualities  from  Sweden  must  be 
used,  such  as  seamless  tubes,  horseshoe  nails,  etc.  On  account 
of  its  purity  this  low  carbon  electric  steel  is  much  less  inclined 
towards  segregation  than  ordinary  low  carbon  steel,  and  on  this 
account  should  be  particularly  used  where  the  highest  require- 
ments of  absolute  certainty  against  brittleness  are  necessary. 

In  the  electric  furnace  construction  steels  of  any  degree  of 
hardness  can  be  produced,  of  any  desired  physical  properties  and 
chemical  analysis,  also  alloyed  with  chromium  and  nickel  where 
it  is  a  question  of  meeting  the  highest  specifications.  These 
steels  at  present  must  be  made  in  the  crucible. 

With  the  large  heats1  possible  in  the  electric  furnace  a  cer- 
tainty of  absolutely  uniform  composition  is  guaranteed  for  the 
finished  steel,  such  as  is  suitable  for  the  production  of  large 
forgings  low  in  manganese.  The  electric  furnace  material  can 
be  easily  hardened,  and  on  account  of  its  homogeneity  and 
freedom  from  slag  is  an  excellent  material  in  such  cases  where 
the  surface  must  be  dense*  and  highly  polished  and  show  no 
cracks,  such  as  running  taps,  etc.  In  general  Plates  3  and  4 
show  what  high  requirements  are  in  every  way  satisfied  by  elec- 
tric steel. 

FINAL  CONSIDERATIONS 

For  the  smelting  of  ore  the  electric  hearth  as  well  as  the 
shaft  furnace  is  to  be  considered,  and  in  each  particular  case  it 
must  be  carefully  decided  which  type  of  furnace  has  the  advan- 
tage. If  very  finely  divided  ores,  high  in  sulphur,  are  to  be  worked 
up  into  steel  by  means  of  small  sized  reducing  material,  then  the 
induction  hearth  furnace  should  be  chosen  because  of  the  possi- 
bility of  producing  steel  direct  from  such  raw  materials  of  any 
quality  desired.  Also  because  when  changes  have  often  to  be 

1  See  Osborne  Amer.  Electro-Chemical  Society,  1911,  Vol.  XIX. 
*  For  quality  of  steel,  see  also  Vom  Baur,  American  Foundrymen's  Associa- 
tion, May,  1911,  page  247. 


THE  ELECTRO-METALLURGY  OF  IRON  AND  STEEL          441 

made  in  the  kind  of  metal  produced,  the  making  of  valueless 
transition  products  is  avoided.  On  the  other  hand,  if  coarse 
low  sulphur  lump  ore  and  fuel  are  available,  then  the  induction 
shaft  furnace  should  be  chosen,  especially  if  the  same  quality  of 
metal  is  always  to  be  made,  and  the  reducing  material  is  high  in 
price. 

The  electro- thermal  smelting  of  iron  ores  can  naturally  only  be 
considered  economically  when  the  saving  of  coke,  etc.,  compared 
with  the  ordinary  blast  furnace  operation  is  greater  than  the  ex- 
pense of  the  necessary  electric  power,  so  that  it  is  dependent  on 
the  local  prices  of  coke,  etc.,  on  the  one  hand,  and  electric  energy 
on  the  other.  Electric  ore  smelting  will,  however,  be  favored 
when  one  considers  that  considerably  less  capital  is  necessary 
for  the  plant  than  for  the  building  of  an  ordinary  blast  furnace 
plant  with  the  same  output.  Also  the  depreciation,  etc.,  per 
metric  ton  of  iron  produced,  are  considerably  lower  than  with 
the  ordinary  blast  furnace. 

It  must  be  further  remembered  that  the  quality  of  electric 
pig  iron  is  higher  than  charcoal  pig  iron,  and  therefore  it  should 
command  a  higher  selling  price  than  the  best  charcoal  iron.  For 
steel  making  an  iron  can  be  readily  made  low  in  silicon,  which 
only  needs  removal  of  carbon  to  make  steel  and  forgeable  metal. 
If  this  refining  is  carried  out  in  the  electric  furnace,  then  it  has 
to  compete  with  the  open  hearth  furnace.  Recently  Engelhardt 
at  the  meeting  of  the  "Verein  deutscher  Ingenieure,"  in  Berlin, 
made  an  interesting  comparison  between  the  open  hearth  furnace 
on  the  one  hand,  and  different  types  of  electric  hearth  furnaces 
on  the  other,  namely  the  Heroult,  the  Girod,  and  the  Induction 
furnaces. 

For  medium  furnace  sizes  with  these  three  types  the  produc- 
tion per  h.p.  day,  with  a  cold  charge,  is  taken  as  20  kg.  Cer- 
tainly this  treats  the  induction  furnace  somewhat  unfavorably, 
for  it  has  about  10%  greater  efficiency.  The  given  power  con- 
sumption corresponds  to  880  kw.  hrs.  per  metric  ton  of  steel. 
The  electrode  consumption,  according  to  the  most  recent  publica- 
tions, amounts  to  28  kg.  per  metric  ton  in  the  Heroult  furnace 
and  17  kg.  in  the  Girod,  while  with  the  induction  furnace,  of 


442  ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 


course,  there  is  not  any.  The  consumption  per  metric  ton  of 
steel  is  therefore: 

With  the  Heroult  furnace  880  kw.  hrs.  +  28  kg  electrode. 

With  the  Girod  furnace  880  kw.  hrs.  +  17  kg.  electrode. 

With  the  Induction  furnace  880  kw.  hrs.  +  o  kg.  electrode. 

In  the  following  table  the  results  of  calculations  are  given  to 
show  how  much  the  kw.  hr.  ought  to  cost  in  order  that  the 
electric  furnace  may  compete  economically  with  the  open  hearth 
furnace  using  a  certain  amount  of  coal  per  ton  at  a  certain  price. 
The  electrodes  are  taken  at  26  marks  per  100  kg.  ($61.90  per 
metric  ton): 


OPEN  HEARTH   FURNACE 

MAXIMUM  COST  PER  KW.  HR.  IN  CENTS  WITH  THE 

Coal 

Price 

Cost  of  coal 

consumption 

of  coal  per 

per  metric  ton 

Girod 

Heroult 

Induction 

by  weight 

metric  ton 

output 

25% 

$3-57 

$0.89 

minus 

minus 

0.1000 

4.76 

I.I9 

0.0143 

" 

0.1333 

5-95 

I.48 

o  .  0476 

" 

o.  1690 

7-14 

I.78 

0.0833 

0.0048 

0.2023 

30% 

3-57 

1.07 

0.0024 

minus 

o.  1214 

4.76 

1.42 

0.0428 

" 

0.1618 

5-95 

I.78 

0.0833 

0.0048 

0.2023 

7-14 

2.14 

0.1238 

0.0452 

0.2428 

35% 

3-57 

1-25 

0.0214 

minus 

0.1404 

4.76 

1.66 

0.0690 

" 

0.1880 

5-95 

2.08 

0.1166 

0.0381 

0.2356 

7-14 

2.50 

0.1642 

0.0857 

0,2832 

40% 

3-57 

1.42 

0.0428 

minus 

0.1618 

4.76 

1.90 

0.0952 

0.0190 

0.2142 

5-95 

2.38 

0.1500 

0.0714 

0.2690 

7.14 

2.85 

0.2047 

0.1261 

0.3237 

It  must,  however,  be  remembered  that  even  when  producing 
an  ordinary  open  hearth  quality  of  steel  in  the  electric  furnace, 
material  is  produced  with  improved  physical  properties  so  that 
even  with  a  continued  regular  output  there  should  be  a  small 
increased  price.  If  this  increase  in  price  is  only  5%,  and  the 
price  per  metric  ton  of  open  hearth  quality  be  taken  as  140  marks 


THE  ELECTRO-METALLURGY   OF  IRON  AND   STEEL  443 


PLATE  II 

Single  Tube  test  piece  from  Plate  I. 


444    ELECTRIC  FURNACES  IN  THE  IRON  AND  STEEL  INDUSTRY 

($33.33),  then  there  is  a  surplus  per  ton  of  7  marks  ($1.66),  which 
with  a  power  consumption  of  880  kw.  hrs.  per  ton  makes  almost 
0.2  cents  that  the  price  of  power  may  be  increased  over  the  value 
given  in  the  table.  It  may  be  further  mentioned  that  the 
electrode  consumption  figures  taken  by  Engelhardt  appear 
somewhat  too  high,  in  view  of  the  most  recent  figures  given  in 
Part  I  of  this  book,  which  vary  from  10  to  15  kg.  per  metric 
ton  of  solid  charge. 

Therefore  the  table  (on  page  304)  may  be  referred  to 
where  the  electrode  consumption,  however,  is  not  considered 
at  all;  and  where  the  heating  costs  alone  are  compared,  on  the 
one  hand  with  the  use  of  fuel  and  on  the  other  with  electricity. 
This  table,  therefore,  gives  results  similar  to  those  in  the  table 
on  the  preceding  page  for  induction  furnaces,  with  which  it 
agrees  exactly. 

The  result  of  all  this  is  that  the  electric  furnace  will  not  only 
play  an  important  role  in  the  future,  but  that  it  is  already  a 
factor  which  each  iron  and  steel  plant  must  now  carefully  con- 
sider. 


INDEX 


Abbreviations  used,  xviii 

Action  of  the  electric  current,  26-44 

Additions,  311,  386 

Advantage,  chief,  of  electric  furnace,  74 

Advantages  of  the  electric  furnace  and  steel,  65-66,  74,  302,  408,  413,  419,428 

Alternating  current,  comparison  single  and  polyphase  generators,  70 

current  theory,  47-63 

polyphase  current  in  general,  60 
Aluminum,  411,  432 
Amperes,  unit  of  measurement,  12 
Angular  velocity  (m  =  2  T:  v),  48 
Applicability  of  the  electric  furnace  (general),  73-74 

of  the  Girod  furnace,  158 

of  the  Heroult  furnace,  144 

of  the  Kjellin  furnace,  204 

of  the  R.  &  R.  furnace,  235  ^ 

of  the  Stassano  furnace,  122 
Arc  furnaces  in  general,  77-79 

heating,  37 

important  points  concerning,  109 

lengths  with  the  Heroult  furnace,  134 
with  the  Stassano  furnace,  119 

temperature  of,  78,  105 

the  electric,  77-79 
Arrangement  of  an  electric  pig-iron  furnace,  247,  364 

of  a  Girod  furnace,  150 

of  a  Heroult  furnace,  129-134 

of  a  Kjellin  furnace,  190 

of  a  Rochling-Rodenhauser  furnace,  209-215. 

of  a  Stassano  furnace,  114 

principle  of  induction  furnaces,  180 

tilting  furnaces  in  general,  72 
the  Girod  furnace,  157 
the  Heroult  furnace,  143 
the  Kjellin  furnace,  203 
the  Rochling-Rodenhauser  furnace,  231 
the  Stassano  furnace,  121 
Arsenic,  406 

Auto-regulating  transformer,  230 
Auxiliary  apparatus,  315,  316 

Basic  bottom  and  lining  material,  296 

445 


446  INDEX 

Basic  bricks,  296 

Basic  laws  of  electricity  and  magnetism,  1 1-25 
Blast  furnace,  total  operating  cost,  comparison,  317 
Booth-Hall  furnace,  276 
Borchers'  laboratory  furnace,  33 

Bottom  electrodes,  influence  of  the  Chapelet  furnace,  257 
of  the  Girod  furnace,  161 
of  the  Keller  furnace,  242 
Bricks,  basic,  296 

carbon,  172 

carborundum  or  silicon  carbide,  295,  322 

Dinas,  295 

dolomite,  296 

half  Schamotte,  295 

half  silica,  295 

magnesite,  296 

silica  or  acid,  295 

Canadian  Commission,  report  of  Haanel  and,  9 
Carbon,  412,  418 

bricks,  172,  295,  302,  322 
electrodes,  their  efficiency,  84 

their  influence  with  the  Girod  furnace,  159 
with  the  Heroult  furnace,  140 
with  the  Stassano  furnace,  117-123 
heat  conductivity  and  specific  resistance,  91 
mixtures  for  lining,  295 

necessary  per  ton  of  pig-iron  for  desulphurizing,  354 
Castings,  electric  steel,  416 
Cast  iron,  low,  phosphorus,  for  thin-walled  castings,  414 

melted  in  electric  furnace  advantage,  414 
Chapelet 's  ore  furnace,  257-258 
Charge,  course  of  operations  of  electric  furnace,  437 

nature  of,  301 
Chemical  action  of  the  electric  current  in  electric  furnace,  37-38 

balance,  for  ore  smelting,  344 
Chrome  iron  ore,  297 
Clay  used  as  a  binder,  294 
Colby  furnace,  185 

medal  for,  in  consideration  of  originality  of  his  furnace,  182 
Cold  charge,  melting  in  the  Girod  furnace,  164 
in  Heroult  furnace,  132-141 
in  Kjellin  furnace,  192-200,  208 

in  Rochling-Rodenhauser  furnace,  232,  235,  223-236,  239 
in  Stassano  furnace,  116 

Combined  arc  and  resistance  furnaces,  79,  260 
resistances,  20 

arithmetical  examples,  21,  22 


INDEX  447 


Comparison  of  costs,  crucible  and  electric,  306 

open  hearth  and  electric,  304,  442 
Compressed  air  hammers,  299 
Conductivity,  12 
Conductor,  resistance  of  a,  12 
Conductors,  action  of  two  on  each  other,  43 
between  magnet  and  electric,  40-41 

of  the  second  class,  15-17 
Construction  of  Girod  furnace,  149 

of  Heroult  furnace,  130 

of  Kjellin  furnace,  189 

of  R.  &  R.  furnace,  213 

of  Stassano  furnace,  1 1 1 
Cooling  of  the  electrodes,  99-102 
Copper,  406 

Cos  <p  influence  of  the  power  factor,  55,  58,  64 
Cost  of  the  auxiliary  apparatus,  315 

comparative,  ordinary  blast  and  electric  pig-iron,  316,  442 

of  depreciation,  314 

of  desulphurizing,  323 

of  electric  pig-iron  furnace  installation,  255 

of  the  electrodes,  315 

installation  of  Girod  furnace,  160 
of  Heroult  furnace,  147 
of  Rochling-Rodenhauser  furnace,  239 
Crawford,  383-403 
Creuzot,  induction  furnace  of,  261 

Crucible  furnace,  heating  with  costs  compared  to  electric,  306 
Current  density  of  electrodes  (general),  82 
Girod  furnace,  159 
Heroult  furnace,  139 
Stassano  furnace,  117 
Currents  permitted  in  wires  and  cables,  29 
Cylinder  winding,  181 

Davy's  experiment,  3 

Delta  connection,  63 

Deoxidation,  428,  429 

Depreciation,  314 

Desulphurizing,  cost  of,  323 

Diagram  of  connections  of  a  Kjellin  furnace,  199 

Dinas,  bricks,  295 

English  or  lime,  bricks,  295 

German  or  clay,  bricks,  295 
Direct  current,  applicability  of,  68 
Dolomite,  296 

plant,  296 
Dynamo  sheet-iron,  60 


448  INDEX 

Economical  considerations,  287-307 
Economy  of  the  electric  shaft  pig-iron  furnace,  250 
Eddy  currents,  59 

Efficiency,  arc  furnaces,  influence  of  the  electrode  consumption  on,  96-99,  238 
of  carbon  electrodes,  84 
electric  (general),  72 

Girod,  furnace,  157 

Heroult  furnace,  142 

Kjellin  furnace,  194,  203 

R. &  R.  furnace,  231 

Stassano  furnace,  121 

electrode,  according  to  C.  A.  Hansen  and  Carl  Hering,  83-99 
graphite  electrodes,  84 
shaft  furnaces,  electric,  241 
thermal,  Girod  furnace,  162 

Heroult  furnace,  146 

R.  &  R.  furnace,  239 

Stassano  furnace,  124 
total,  Girod  furnace,  160 

Heroult,  furnace,  146 

Kjellin  furnace,  207 

R.  &  R.  furnace,  237 
Electric  conditions  of  a  Girod  furnace,  152 

of  a  Heroult  furnace,  134 

of  a  Kjellin  furnace,  194 

of  a  Rochling-Rodenhauser  furnace,  227 

of  a  Stassano  furnace,  121 
furnace,  demands  of  an  ideal,  66-73 
furnaces,  advantages  of,  65-66,  74,  302,  428 
pig-iron,  characteristics  of,  438 
power,  cost  of,  311 

steel,  high  quality  characteristics  of,  427 
steel  production  in  principal  countries,  307 
Electrode  arrangement  with  Girod  furnace,  150 

with  Heroult  furnace,  131 
cooling,  99 

consumed  by  Stassano  furnace,  124,  319 
consumption  (general),  96-97 

with  Girod  furnace,  162 

with  Heroult  furnace,  134 

with  shaft  furnace,  254 

influence  on  furnace  efficiency,  81-83 
cost,  315 
covering,  98 
cross-section,  comparison  with  Girod  and  Heroult  furnaces,  159 

influence  of,  80-82,  93 
losses  (general),  89 

lowest  total,  86-90 


INDEX  449 

Electrode  losses,  with  Girod  furnace,  159 
with  Heroult  furnace,  135-136 
with  the  Stassano  furnace,  118 
of  pole  plates  R.  &  R.  furnace,  228 

pole  plate  consumption  with  Rochling-Rodenhauser  furnaces,  227 
pole  plates,  with  R.  &  R.  furnace,  214 
regulation,  general,  102 
Girod  furnace,  156 
Heroult  furnace,  131 
Stassano  furnace,  120 
Electrodes,  for  arc  furnaces,  80-102,  168 
consuming,  the,  89 
with  Stassano  furnace,  117-124 
Electro-metallurgy  of  iron,  335 
Electro-metals  shaft  furnace,  243,  326,  339 
Elliott,  416,  420 

Energy  regulation  of  the  Girod  furnace,  157 
of  the  Heroult  furnace,  131 
of  the  Kjellin  furnace,  201 
of  the  R.  &  R.  furnace,  230 
of  the  Stassano  furnace,  117,  120,  122 
Expansion  of  the  refractories,  294 

Ferranti,  de,  furnace,  181-182 
Ferro  alloys,  408-410 
Ferro-chromium,  408-410 
Ferro-manganese,  408,  410,  412 
Ferro-silicon,  408-410 

required  for  desulphurizing,  333 
Fluor-spar,  4 1 1 

Flux,  to  lower  melting  point  of  refractories,  298 
Fluxes,  312 
Foucault  currents,  59 
Frequency,  47,  48,  50 

with  what,  shall  the  electric  furnace  operate,  70 
Frick  furnace,  185 

and  Kjellin  furnaces,  differences,  186 
Furnace,  at  Allevard,  257 
refractories,  292-299 
size  attainable  with  Girod  type,  159 
with  Heroult  type,  146 
with  Kjellin  type,  206 
with  R.  &  R.  type,  237 
with  Stassano  type,  121 
system,  its  influence  on  the  quality  of  steel  made,  298 

Galvanized  electric  steel  sheets,  305 
Giffre  furnace,  see  Chapelet  furnace,  257 
Gin,  induction  furnace  of,  263 


450  INDEX 

Gin,  resistance  furnace  of,  28 

arithmetical  example  of,  28-29 
Girod  furnace,  the,  149 

action  of  the  heat,  154 

advantages  of,  164 

applicability,  158 

arrangement,  149 

arrangement  of  electrodes,  149 

attainable  size,  159 

circulation  in  the  bath,  157 

comparison  with  an  ideal  furnace,  156 

cost  of  a  furnace,  161 

crucible,  34 

current  density  in  the  electrodes,  159 

electrical  conditions  with,  152 

electrical  efficiency,  157 

electrode  cross-section,  159 
losses,  159 

electrodes  consumed,  162 

historical,  149 

influence  of  bottom  electrodes,  154-158 

influence  of  the  carbon  electrodes,  160 

installations,  161-163,  291 

kind  of  current  used,  153 

licenses,  giving,  164 

operation,  152 

power  fluctuations,  156 

power  used,  157-158 

refractories,  150 

regulating  energy  of,  157 

thermal  efficiency,  162 

the  tilting,  150-157 

total  efficiency,  160 

operating  cost,  320 

Graphite  and  carbon  electrodes,  comparison  between,  90-98 
electrodes,  efficiency  of,  84 
heat  conductivity  and  specific  resistance,  90 
Gray,  J.  H.,  324 
Greaves-Etchells  furnace,  265 
Gronwall  arc  furnace  for  steel,  264 
induction  furnace  for  steel,  264 
Lindblad  and  Stalhane  electric  shaft  furnace,  247 

hearth  furnace  for  smelting  ore,  241,  256,  361,  381 

Haanel  and  the  Canadian  Commission's  report,  9 
Half  Schamotte  bricks,  295 

silica  bricks,  295 
Hearth  arrangement,  general,  73 


INDEX  451 

Hearth  arrangement  of  the  Girod  furnace  157 
of  the  Heroult  furnace,  143 
of  the  Kjellin  furnace,  204 
of  the  R.  &.  R.  furnace,  23 1 
of  the  Stassano,  109,  122 
bottom  with  the  Kjellin  furnace,  191 
with  the  R.  &  R.  furnace,  217 
with  the  Stassano  furnace,  114 
form  and  life  of  refractories,  299 
Heat  action,  26-35 
balance,  345 
conductivity  of  carbon,  91 

of  graphite,  91 
losses,  86-87 

quantities,  relations  electrical  and  mechanical,  24-25 
required  for  ore  reduction,  332,  339 

Heating  costs,  comparison  of  blast  and  electric  pig-iron  furnace,  316 
of  crucible  and  electric,  306 
of  open  hearth  and  electric,  304,  442 
influence  present  with  arc  furnaces,  38 

with  electric  furnaces  in  general,  73 
with  induction  furnaces,  188 
with  the  Girod  furnace,  154 
with  the  Heroult  furnace,  131 
with  the  Kjellin  furnace,  199 
with  the  R.  &  R.  furnace,  213 
with  the  Stassano  furnace,  112,  119 
the  Heroult  furnace,  138 
the  Kjellin  furnace,  192 
the  Rochling-Rodenhauser  furnace,  222 
the  Stassano  furnace,  1 19 
Helberger  crucible  furnace,  35 
Heraus  laboratory  furnace,  34 
Heroult  furnace,  125 

action  of  the  heat,  131 

advantages  of,  147 

applicability  of,  144 

arc  length  of,  133 

arrangement  of  elecrodes,  129 

attainable  size,  144,  146 

circulation  in  the  bath,  144 

comparison  with  an  ideal  furnace,  139 

cost  of  a  furnace,  147 

current  density  in  electrodes,  134 

current  fluctuations,  131 

electric  conditions,  132 

electrical  efficiency,  142 

electrode  cross-section,  134,  137" 


452  INDEX 

Heroult  furnace,  electrode  cross-section,  losses,  135-136 

electrodes  consumed,  137,  145,  322 

historical,  125-127 

influence  of  carbon  electrodes,  141 

installations,  128,  291 

kind  of  current  used,  145 

licenses,  giving,  148 

operating  cost  of  1 5-ton,  145 

operation  of,  138 

power  fluctuations,  132 

power  used,  136,  139-140 

regulating  of  energy,  130,  131 

refractories  and  roof,  146,  323 

thermal  efficiency,  146 

the  tilting,  142 

total  efficiency,  146 
Hiroth  furnace,  254 
Historical  in  general,  l-io 
of  the  Girod  furnace,  149 
of  the  Heroult  furnace,  125,  243 
of  the  Kjellin  furnace,  189 
of  the  Rochling-Rodenhauser  furnace,  209 
of  the  Stassano  furnace,  no 
Howe,  criticism  of,  300,  301 
Hysteresis  losses,  60 

Ideal  electric  furnace,  compared  to  a  Girod  furnace,  156 
to  a  Heroult  furnace,  139 
to  a  Kjellin  furnace,  201 
to  a  R.  &  R.  furnace,  228 
to  a  Stassano  furnace,  120 
demands  of,  65-72 
Impurities  in  the  charge,  getting  rid  of,  74 

in  iron,  400 
Induced  current,  176 

E.  M.  F.  and  its  size,  179 
Induction,  49 

furnaces,  combined,  188 

important  points  concerning,  187-188 
in  general,  176-188 
of  Gin,  263 

principal  arrangement,  181 
pure,  181-184 
heating,  32 

characteristics,  180 
losses  due  to  phenomena,  51-53 
Installation  at  Aarau  (Girod),  161 
at  Allevard  (Chapelet),  257 


INDEX  453 


Installation  at  Bonn  (Stassano),  117 

at  Chicago  (Heroult),  136 

at  Dommeldingen  (Rochling-Rodenhauser),  211 

at  Essen  (Frick),  186 

at  Essen  (Kjellin),  207 

at  Friedenshiitte  (Nathusius),  260 

at  Gysinge  (Kjellin),  199 

at  La  Praz  (Heroult),  128 

at  Remscheid  (Heroult),  129 

at  Ugine  (Girod),  164 

Volklingen  (Rochling-Rodenhauser),  226 
Installations,  statistics  of  electric  steel  furnace,  291 
Instantaneous  values,  48-50 
Iron,  gray,  avoidance  bad  heats  in  electric  furnace,  415 

ore,  410 

reduction  from  iron  pyrites,  340 

resistance  of  cold,  14 
of  molten,  15 

Joule's  law,  23 
Joule  losses,  81 

Keller,  arc  furnace,  258 

pig-iron  furnace,  242 
Kirchhoff's  law,  19 
Kjellin  furnace,  9;  189 

action  of  the  heat,  199 

advantages  of,  204 

applicability  of,  204 

attainable  size,  206-207 

circulation  in  the  bath,  204 

cooling  of  parts,  191-192 

comparison  with  an  ideal  furnace,  201 

current  fluctuations,  190,  193,  201,  202 

electrical  conditions,  194,  195 

electrical  efficiency,  198,  203 

frequency,  lowering  of,  196 

historical,  189 

installations  of,  291 

licenses,  giving,  for,  208 

operation  of,  192,  200 

pinch  effect,  206 

Poldihutte,  improved  bottom,  206 

power  factor,  194,  196,  197 
fluctuations,  202 
used,  208 

refractories  and  roof,  191 

regulation  of  energy,  201 

thermal  efficiency,  208 


454  INDEX 

Kjellin  furnace,  tilting  type,  192,  203 
total  efficiency,  207-208 
transformer  of,  189 
and  Frick  furnaces,  the  differences,  186 

Labor,  312 

Laboratory  furnace  of  Borchers,  33 

of  Heraus,  34 
Latent  heat  of  fusion  of  pig-iron,  339 

of  slag,  339 

Laval,  de,  electric  furnace  of,  7 
Licenses,  giving,  for  Girod  furnaces,  163 

for  Heroult  furnaces,  148 

for  Kjellin  furnaces,  208 

for  R.  &  R.  furnaces,  240 

for  Stassano  furnaces,  124 
Lime,  410 

Dinas  bricks,  295 
Line  diagram,  47 
Lining,  preventing  attack,  426 
Loss,  melting,  302 
Ludlum  electric  furnace,  284 
Lyon  furnace,  369       x 

Magnesite,  297 

bricks,  297 

Magnet,  action  between,  and  electric  conductor,  40 
Magnets,  action  of  two  on  each  other,  40 
Magnetic  lines  of  force,  direction  of,  41 

field  of,  cut  by  a  conductor,  42 
of  a  coil,  43 

Magnetizing  currents,  40 
Malleable  iron  castings,  415,  416,  420 
Manganese,  absence  of  loss  in  electric  furnace,  413 

ferro,  less  needed  for  deoxidation  if  liquid,  408 
Material  charged,  301 

for  furnace  construction,  291 
Maximum  values,  48 

Medal  for  Colby;  his  induction  furnace,  182 
Melting  pig-iron,  413 
Mixer,  electric  furnace  as  a,  422 
Moldenke,  416 
Moore  furnace,  274 
Mortar,  297 
Motor  effect,  action  of  the  electric  current,  39 

Nathusius,  arc  furnace  of,  260,  275 
Neutral  point,  63 


INDEX  45T) 

Ohm's  law,  11-12 
Ohm,  the  unit,  12 
Open-hearth  furnace  and  electric,  comparison  of  their  heating  costs,  304,  305, 

442 

Operating  costs  of  the  electric  shaft  and  ordinary  blast  furnace,  301,  319 
of  the  Girod  furnace,  157-158,  320 
of  the  15-ton  Heroult  furnace,  322 
of  the  Rochling-Rodenhauser  furnace,  324 
of  the  Stassano  furnace,  319 

Operation,  general  requirements  for  electric  furnace,  65-75 
of  electric  shaft  furnaces,  316,  317 
of  the  Girod  furnace,  152 
of  the  Heroult  furnace,  137 
of  the  Kjellin  furnace,  192,  200 
of  the  Rochling-Rodenhauser  furnace,  237,  324 
of  the  Stassano  furnace,  1 16-1 17 
Ore  reduction,  heat  required  for,  331 
smelting,  328-348 

criticism  of,  in  the  electric  hearth  furnace,  348 
in  the  electric  shaft  furnace,  351 

of  Gronwall,  Lindbald  and  Stalhane,  338 
in  the  hearth  furnace  of  Gronwall,  Lindblad  and  Stalhane,  381 

of  R.  &  R.,  339 

in  the  special  furnace  of  Heroult,  355 
in  the  Stassano  furnace,  335 
in  the  test  furnace  of  Lyon,  373 
Osborne,  440 
Oxygen,  407 

Parallel  connection,  16-22 

Pepys"  test,  4 

Period,  periodicity,  47-50 

with  what  shall  the  electric  furnace  operate,  70 
Phase  current,  63 

displacement,  54 

its  influence  in  a.  c.  circuits,  55-58 

voltage,  63 
Phosphorus,  400 
Pichon,  electric  furnace  of,  4 
Pig-iron,  carbon  required  per  ton,  354 
Pinch  effect,  44,  206 
Pipe  casting,  414 
Pneumatic  hammers,  299 

Poldihutte,  improvements  in  lining  and  bottom  for  Kjellin  furnace,  206 
Pole  plate  electrodes  with  R.  &  R.  furnace,  112,  315 
Power,  apparent,  55 

cost  of  electric,  per  kw.-hr.,  287 

effective,  54 


456  INDEX 

Power,  factor,  arithmetical  example,  56 

influence  of  the,  194 

with  Kjellin  furnaces,  influence  of  charge  on,  194 
fluctuations,  influence  of,  71 

with  the  Girod  furnace,  156 

with  the  Heroult  furnace,  131 

with  the  Kjellin  furnace,  193 

with  the  Rochling-Rodenhauser  furnace,  117,  225 

with  the  Stassano  furnace,  120 
generating  cheap,  68,  287 
table  for,  24-25 
three-phase  circuit,  63-64 
used  and  its  influences,  244 

with  the  electric  pig-iron  furnace,  255 

with  the  Girod  furnace,  158 

with  the  Heroult  furnace,  138 

with  the  Kjellin  furnace,  208 

with  the  R.  &  R.  furnace,  239 

with  the  Stassano  furnace,  124 

Quality  characteristics  of  electric  iron  and  electric  steel,  427,  438" 
of  the  steel,  influence  of  the  furnace  type  on,  305 
steel,  making  it  in  the  electric  furnace,  395,  427 

Quartz,  294 

Quartzite,  294 

Quick  melting,  advantages  of,  208,  308 

Radiating  furnaces,  79 

Reasons,  economical,  for  introduction  of  electric  furnace,  427 
Refining  of  pig-iron,  423 
Refractories,  coet  of  the,  301 
of  the  Girod  furnace,  150 
of  the  Heroult  furnace,  143,  323 
of  the  Kjellin  furnace,  191 
of  the  R.  &  R.  furnace,  212,  217,  224 
of  the  Stassano  furnace,  114,  119 
Refractory,  durability,  and  hearth  form,  298 
material  is  called,  when,  293 
materials,  292,  299 
mixtures,  296 

Regulating  or  auto-transformer,  230 
Regulators  (automatic)  for  electrodes,  102 
Rennerfelt  furnace,  165-175 

action  of  the  heat,  166,  168 
advantages  of,  173 
applicability,  171 
arrangement,  166,  170 
attainable  size,  166,  171 


INDEX  457 


Rennerfelt  furnace,  circulation  of  the  bath,  171 

comparison  with  ideal  furnace,  168-172 

cost  of  a  furnace  and  parts,  171,  173 

current  density  in  the  electrodes,  169-170 

electrical  conditions  with,  167 

electrical  efficiency,  171 

electrode  cross-section,  168 
losses,  i/o 

electrodes  consumed,  172 

historical,  165,  175 

intermittent  operation,  171 

kind  of  current  used,  168,  169 

licenses,  175 

operation,  168 

power  fluctuation,  167,  170 

power  used,  168,  169,  172,  173 

refractories,  164,  168,  171,  172 

regulating  energy  of,  167,  170,  173 

thermal  efficiency,  172 

tilting,  171 

Resistance,  apparent,  54 
of  a  conductor,  1 1 
of  carbon,  specific,  91 

change  in  graphite  and  carbon  electrodes,  94-95 
of  graphite,  specific,  91 
heating,  characteristics,  31-32 

direct  and  indirect,  25-32 
specific,  13-15 
Revolving  furnace,  112-122 
Richards,  J.  W.,  235,  272,  273,  301,  318,  345 
Roasting  furnace,  112-122 

of  ores,  366 
Rochling-Rodenhauser  furnace,  213 

advantages  of,  209-210,  226 

applicability  of,  235 

attainable  size,  237 

circulation  in  the  bath,  231 

comparison  with  ideal  furnace,  228 

cooling  of  parts,  215,  216,  228 

cost  of  a  furnace,  239 

cost  of  heat,  212,  219 

current  fluctuation,  225 

electrical  conditions  in  the,  227 

electrical  efficiency,  230,  231 

historical,  209 

installations  of,  290,  292 

kind  of  current  used,  239 

licenses,  giving,  for,  240 


458  INDEX 

Rochling-Rodenhauser  furnace,  operation  of  and  cost,  324 

ore  smelting  in,  339 

power  fluctuations,  225 

power  used,  239 

refractories  and  roof,  217,  222,  234 

regulation  of  energy,  43,  230 

scrap  melting  in,  221,  224,  236,  239 

secondary  circuit,  217,  221,  228 

shut  down  over  Sunday,  225 

slag,  absence  of,  in  channels,  212,  223 

thermal  efficiency,  239 

tilting  type,  213,  231 

total  efficiency,  237-239 

transformer  of,  213 
Roof,  life  of,  with  arc  and  induction  furnaces,  314 

with  Girod  furnace,  320 

with  Heroult  furnace,  144,  323 

with  Rochling-Rodenhauser  furnace,  333 

with  Stassano  furnace,  1 1 7 

Seger  cones,  292 

Series  connection,  18-24 

Shaft  furnace,  electric,  241-255 

economy  of,  254,  310,  382 

efficiency,  254,  318,  319 

electrodes  consumed,  250,  317,  319,  382 

kind  and  quantity  of  carbon  on,  255 

power  consumption,  319,  384 

of  Gronwall,  Lindblad  and  Stalhane,  247,  361,  381 

of  Heroult,  243,  354 

of  Keller,  241-242 

of  Lyon,  373 

of  Stassano,  241 
Silicon,  406 

carbide  bricks,  172,  295,  322 
Snyder  furnace,  269 
Specific  heat,  339 
Star  connection,  62 
Stassano  furnace,  110-124 

action  of  the  heat,  118 

advantages  of ,  121 

applicability  of,  122 

arc  length,  118,  119 

arrangement  of  electrodes,  114-115 

attainable  size,  122 

circulation  in  the  bath,  113,  122 

comparison  with  an  ideal  furnace,  120 

cooling  arrangements,  115 


INDEX  459 

Stassano  furnace,  cost  of  a  furnace,  124 

current  density  in  electrodes,  117,  118,  122 
current  fluctuations,  117,  120 
electric  conditions,  121 
electrical  efficiency,  121 
electrode  cross-section,  117 

losses,  118 

electrodes  consumed,  124,  319 
energy  regulation,  120 
hearth  furnace,  121 
historical,  no 

installations,  117,  291  Ll  if  A  111  | 

kind  of  current  used,  121 


licenses  given,  124 
operation  of,  116,  117 
operation  cost,  124 
ore  smelting,  335 
power  used,  124 
power  fluctuations,  120 


Los  Angeles,  Galif 


refractories  and  roof,  1 14,  1 19 

regulating  of  energy,  117,  120,  122 

rotating,  112 

shaft,  or  pig-iron  furnace,  no,  241.  335 

thermal  efficiency,  124 

tilting,  121 
Statistics  of  electric  furnaces,  291 

and  steel,  307 
Steel,  bad,  non-expert  handling,  436 

castings,  electric,  122,  291 
Straying,  177-187 

method  of  lessening  the  straying,  187 
Sulphur,  345,  402 

Tar,  296 

Taussig,  electric  furnace  of,  8,  26 

Temperature  coefficient,  14,  15 

regulation  of  electric  furnaces,  72 

with  electric  heating,  73 

Thin-walled  castings,  gray  iron,  low  phosphorus,  414 
Three-phase  current,  61 
Titanium,  409 
Tools  used,  299,  301 
Transformer  (principal  arrangement),  178-180 

coefficient,  179 

iron,  60 
Tube  winding,  181 

Unburnt  slag,  294 
Units,  electrical,  12 


460  INDEX 

Values,  instantaneous,  48-50 

Vanadium,  409 

Vector  diagram,  51 

Very  refractory,  293 

Volt,  unit  of  electrical  pressure,  12 

Vom  Baur,  166,  175,  183,  217,  440 

furnace,  279 

advantages  of,  280 

arrangement  of  electrodes,  280 

attainable  size,  282 

hearth  of,  280 

refractories,  280 

shape,  280 

tilting,  281 

Water  cooling,  influence  of,  75 
Watt  component,  57 
Wattless  component,  57 
Wattmeter,  57-64 
Work,  table  for  delivered,  25 

Zirconia  brick,  296 


THE  LIBRARY 

DIVERSITY  OF  (  VUFORNU 
LOS  ANGELES 


TN 
706 
R61e 
1920 

Engineering 


UMtt 

STACK 

SEP      '73 


